Any experienced exhaust Guru out there?
I have been reading, and working (above my head) with all sort of calculations, to formulate the perfect exhaust system for my MGB powered by a Ford small block (331) stroker. Having said that, the reality is that having the wrong mufflers or pipe size can defeat the perfect induction system.
Combustion chamber filling doesn't only depend on the intake side for maximizing fresh intake mixture volume; in fact, the low pressure developed by a strong scavenging exhaust system is the main contributor to pulling in the next batch of fresh oxygen rich air charge.
Some racers find it more difficult to fine tune the exhaust extraction to maintain a lengthy low pressure scavenging trail than it is to formulate the induction system. BTW, maintaining back pressure turns out to be a myth, it has nothing to do with fine tuning exhaust formulas.
So far, I'm thinking that the section immediately following my headers (through fender well) is the critical area to good scavenging. The problem is that on the MGB, there's a sharp turn following the collectors, so I'm using as long a radius as possible with a 2-1/2" pipe (all the way to the back)
I'm trying to generate ideas from members that have been there (FSB) and have some trial and error experience with the MGB short wheel base and the exhaust. How about an "X" pipe? Its benefit are credible, however, there's not much room to accommodate it; what mufflers can excel on flow attributes while maintaining a civil rumble?
I know that some of you may think that I'm over thinking this one, but, after seeing some dyno numbers based on exhaust change (gain or lost), it got me convinced that your engine's performance (and MPG) relies on a strong partnership between the intake and exhaust systems. Please let me know your thoughts on it.
Jacques
QuoteI know that some of you may think that I'm over thinking this one
Jacques,
There's no such thing as over thinking. In the end, you may wind up going the same tried and true route as others, but the time spent learning is NOT time misspent.
Jacques, I think you are right about what you said, but have left out one critical element, namely the camshaft. It has a radical effect on both intake and exhaust and the systems that are ideal for one cam will be all wrong for another. So the very first thing that you have to do is to define the performance parameters of the car and determine the rpm range that the car will spend most of it's time in, then also how wide that band is and how "peaky". For instance a highway cruiser might spend 90% of the time (or even more) in a very narrow band centered around or somewhat below 2000 rpm. That use band would be extremely peaky. A car driven only in the mountains might be constantly going between 1500 rpm and 5000 rpm so it's use band would be much flatter. Most are somewhere in between.
Once that is determined a suitable cam for the car can be selected with lift, duration, and overlap that are calculated to enhance the desired operating conditions with emphasis on performance or economy or driveability, or torque within the use band, etc. Only then do you really have enough information to properly design the induction and exhaust system.
Where in the induction system much attention is paid to mass flow, in the exhaust it helps greatly to think in terms of pulsed flow. All extractor type exhaust systems, from a dirt bike to the most complex headers rely on this dynamic, primarily because the exhaust pulse is vented from a pressurized chamber. So how you handle this slug of exhaust gas will determine what happens when the intake valve opens, as well as how much the conditions will vary with engine speed.
Back to the dirt bike, these engines are renowned for a peaky powerband, primarily because the pipe is tuned to provide the greatest possible suction volume at the exhaust port at a particular rpm, known as being "on the pipe" and they create tremendous power at that engine speed, but can be absolute dogs below that.This would be bad in a street driven car. By contrast, the old and poorly appreciated cast iron log manifold, precisely because it is incapable of being tuned to a precise range, gives a very flat performance curve which, it turns out is just what you usually want in an average passenger car. The curve is low and about all you can do to raise it is increase the size of the passages, remove obstructions, and smooth corners to increase flow but you are making almost no use of scavenging whatsoever, with the result that the engine will produce a flatter torque band. For something like, oh I don't know, maybe a really big engine in a really small car like the MG-Roadmaster that was going to be driven in the mountains a lot, this would be an excellent idea. But unless you really do have excess displacement most people will opt for a more performance oriented solution. But note, "performance" in this sense almost always equals a more peaky powerband in some degree. It's just one of those compromises we always have to make. Note that the type of exhaust system used will have a big impact on how much overlap is used in the cam, where a very peaky exhaust can be moderated somewhat by less overlap, etc.
So leaving header/manifold design for later, you next have a series of pulses moving towards the muffler. Usually they are not evenly spaced, and can be thought of as areas of greater density separated by areas of lesser density, some closer together and some farther apart and getting larger or smaller based on engine speed and load. By the time they have passed through the muffler they have been partially merged as well as cooled a bit which is why it is common to see a smaller tailpipe than the header pipe. Muffler design can be complex but basically the size of the box determines the frequency band of attenuation, which is why a large under body muffler and a smaller resonator is a popular combination. The crossover pipe seeks to even out the exhaust pulses, with the X pipe being the most effective means of doing so. However it does require equal length header primary tubes for maximum effectiveness. Bear in mind, the firing sequence causes problems with these pulses which is why the crossover is desirable at all and if you look carefully at the firing sequence you will see why this is so.
Next, pipe size is directly related to engine size and operating speed. The modern trend is towards big pipes but it is clear that this is a trend which favors high speed, heavily loaded applications. From the '70s muscle cars it was very clear that upwards of 300 hp was easily supported by a header down pipe size of 2-1/4" and a 2" tailpipe, and in fact this was almost the standard. The point being that bigger pipes can be used if desired and may help produce more peak power, but could potentially narrow the torque band a bit. At the same time, the exhaust system as a whole will have one resonant frequency where it is most efficient. Larger pipes move this point up the rpm band which is good for power but not necessarily good for economy. For that the exhaust is often tuned to the peak of the use band.
So that is maybe a useful starting point.
JB
Jim, I'm with you. The system needs to be thought of as a whole.
Too many "builders" buy into the hot part of the moment mentality and end up disappointed.
We also have the fuel injected and carbed camps. What works for one does not work for the other. Sewer pipe sized exhaust on an FI car works OK, it's a disaster on a carbed car.
You are clearly a "been there done that" guy and I think your 2-1/4 recommendation is right on.
Jacques you are absolutely on the right path by thinking the whole engine through from air cleaner to tailpipe. But judging from your post you haven't decided what you want your car to do. You mention racing tuning, street manners and mpg. It's like the old saying, you can have your car "good" "fast" and "cheap" pick any two. But tuning your air management system is even more restricted, pick any one and a quarter.
If your tuning for racing then it all boils down to header and collector dynamics. Which become pretty straight forward when you're aiming for specific hp/torque/rpm targets. Exhaust pipes and mufflers don't enter the picture.
Tuning for mpg is a very interesting subject and while optimizing the drivetrains efficiencies is the path to greater hp I don't think you built a 331 to be a gas miser.
That leaves us with the street. In the real world,not the magazine Disneyland, a really good two valve 331 might get 350 hp on a good day. (We really should be talking torque but hp is so much cooler)
Dual 2" pipes will flow enough air to support 400 hp or so. With decent mufflers attached this will probably drop to around the 350 hp range. Add in a few bends and we're looking at 300/325hp. This would be a good choice if mpg trumps ultimate hp. Exhaust temps at the tail pipes will still be nice and high which indicates good velocity and aids longevity.
Dual 2-1/4 pipes will cover 450-500 hp. Add some bends and a couple of good mufflers and you can pass 375hp. This should cover your engine nicely and not be so big as to reduce valuable ground clearance and slow down the exhaust into the problematic range. As a side note a single 3" will flow as much as the dual 2-1/4s due to the reduced surface area despite the greater volume of the duals. However a 3" exhaust would require your mg to become an SUV.
Unless your using 180 degree headers, rate your mufflers on CFM not pulse tuning. I don't want to cause trouble but, Flowmasters flow like crap. Dynomax turbos flow very well and Magnaflows sound awesome.
Crossovers will help a compromised system and make the engine sound more rev happy. An H pipe seems to be better power wise. Think about the straight through nature of it vs the 90' bend required for each side of an X pipe. But the X pipe sounds smoother.
As far as tailpipes go, a smaller pipe ie. a 2" pipe on a 2-1/4 system will give the exhaust that old timey RRRap sound. A bigger pipe IE. a 3" on a 2-1/4 system will give it that boom sound that makes the engine sound bigger than it is.
In the end you can throw numbers at it all day long but what matters is
"does it work or not"
Anyway that's my take on it.
Cheers
Fred
Side pipes anyone ? Better ground clearance. Properly designed to reduce air getting under car,(crude skirt).Less heat transfer onto floor boards. Lastly, looks ? roverman.
I've done that. So has Joe Scheaffer. We agree it'd be hard to go back, but there are real disadvantages too. Aside from being noisy, getting fumes in the car is a real pain, especially sitting at a light with just the right crosswind. I'll be taking a real hard look at routing a tailpipe along the same path used in the MG-Roadmaster. On mine I think it can be done, but it has fully enclosed sidepipes. On that system heat is an issue that must be dealt with.
JB
JB and Fred,
I appreciated your posts.
I'm building a 'Nasty-Boy' 1958 Austin Healey 100-6 two seat roadster. Also employing a 331 SBF like Jacques. Have also procured a narrowed Currie built 8 inch Ford rear-end with TrueTrac & 3.55 gears, and a Tremec TKO-600 5 speed trans with the shorter legged OD 5th gear. Rear tires are 225/60/15s on 15x7 Dayton Wire wheels.
On the dyno, my engine peaked at 400 bhp @ 5800 rpm / 416 lb-ft @ 4200 rpm. Report starts at 2800 where it was 375 lb-ft and 200 bhp, and closed out at 6000 with 350 lb-ft and 398 bhp. Has a forged steel crank, forged pistons, Edelbrock aluminum heads and intake, a tuned 'Stage 2' Holley 650, a 'mild' Comp Cams Hydraulic Roller Cam kit, and all the other standard goodies to hold it together.
The combination employed is meant to deliver a nice smooth, strong torque curve, and I think this goal has been accomplished to date. I want to keep it that way!
I too am researching exhaust options... And given the age of the car, cats are not an issue even in California (yeah!), where I grew up and hope to drive the car when it is done (presently living in exile in a suburb of Pittsburgh, PA - "the Paris of Western Pennsylvania"). Because I expect you'll ask or assume - yep, the engine is going to mostly live between 1500 rpm and 3000 rpm with only the occasional run up to 6000 rpm when embarrassing random German and Italian steel - but I want to be sure the engine will get to well past 5500 rpm long before it starts to choke itself off.
Trying to find a nice set of short tight center dump headers to clear mounts and such... Engine is bolted low and flat parallel to the ground to a custom Jule Enterprises frame (rails 17 inches apart and 23 inches on the outside - engine mounts are customized very stout units meant for a biscuit type combination, but mated to a pair of C5 Corvette hydraulic mounts that bolt directly into the frame rails). From what I've read in notes by David Vizard (a guru), header tuning isn't that important on a street bound V8 (where this will live - hell this thing is going to have AC...) - his reference engine for what I read was the Chevy 350. Any header recommendations..?
Also trying to design a complete system that will not rob too much from the 'go-fast' side of the equation while keeping the noise to a real minimum. I've read about really quiet 'three-muffler' systems used on big Turbo-Buick 10 second dragsters that are so quiet you can barely tell the engine is running (see: http://www.turbobuick.com/forums/general-turbo-buick-tech/167389-3-mufflers-quiet-system.html)! That is my 'goal' - super quiet performance.
Thinking a pair of DynoMax Super Turbo mufflers with an 'H' pipe - maybe a DynoMax 'X' if I can make it fit... I understand that the implementation of either an 'H' or an 'X' will both increase bhp and quiet down the exhaust if properly employed.
Thinking of starting with 2 1/4 pipe from the headers back and running 2 inches out from the mufflers to some sort of shiny tips...
But what about resonators - placement and dimensions?
And how far back should they be from the headers?
I understand the 'H' pipe (or 'X' pipe if I choose that route) should be as close to the headers as possible (and in the case of an 'X' pipe should be sure to be made to look to the gasses like an extension of the tuned-length from the headers). Does this hold true if resonators are employed?
Any recommendations on type of resonators (the Turbo-Buick guys used some sort of 'plane-jane' Summit Racing stuff)?
I've also read the trick is to use the resonators as the end of the tuned-length section from the headers, but the dump into the resonator has to be properly designed for the gas in the pipe to not think the resonator is just an extension of the tuning pipe... I can figure that part out from what I've read, but haven't seen a good formula for calculating the length of the tuning-pipe from the headers... Got one?
Getting going off the line is not my greatest concern, but pulling away with smooth power delivery (not peaky-spikey) is something I want to keep and enjoy....
Any suggestions or guidance would be very appreciated!
Again, enjoyed your thoughtful posts gentlemen!
Regards,
Mark
WOW! Thanks Jim and Fred, I feel like I'm revisiting my exhaust tech article all over again; well said. I've originally started reading this tech info on Sanderson's website:
http://www.sandersonheaders.com/The-Complete-Performance-Exhaust-System.html
Then I went on searching various tech articles and publications. I've failed to mention that my goal targets mostly street cruising and an occasional street light stand off for fun.
Fred, I'm curious as to why you would assume that I would seek a gas miser out of a 331? This light weight fun little car with hidden muscles that carries modern fuel management will do a fine job at managing fuel consumption under light throttle; that's the beauty of modern EFI horse power, it has thought us that fuel efficiency through proper computing, is horse power. My friend has a 2004 Corvette with the base line 400 H.P. "LS engine" that cruises at 28 M.P.G., lots more cubic inches than my 331.
Jim, all you said, concerning the camshaft choice is dead on target. I'm using the old reliable Ford Racing E-303 bump stick in EFI form. It is older technology, but well proven for my needs, it also seems that a lot of existing data revolves around it.
A couple of areas not mentioned that can enhance/tune the given specs of a camshaft are the rocker ratio and the crankshaft small timing gear (slotted to advance or retarded power curve). I wish that there was a way to install a camshaft phaser (variable valve timing) so the choice of power band and R.P.M. would no longer be a problem.
I've installed a full roller rocker with a 1.72 ratio, hence, the duration is now a bit longer and will actually (IMHO) enhance cylinder fill if it exist in harmony with the exhaust resonance (again IMHO), I could be wrong on my calculation/assumption.
It is very true that pipe size are in direct relation to engine cubic inches, however, you should mostly size the diameter based on the desired horse power (see The Sanderson chart) and just like an intake runner that is sized too big will kill (poor air velocity) the low end torque, an exhaust pipe sized too big will also kill the velocity necessary to produce scavenging (trailing) low pressure. Again, with assumptions based on engine improvements, 2-1/2" piping is within the rules of given specs. Again, take a look at Sanderson's pipe size chart; it matches all responses given on most respectable Mustang web forums.
Lets not get into forced induction as it changes a lot of rules, but, mufflers designed around turbochargers, hence "Turbo muffler", seems to be a decent choice because of its lower flow restriction, however, it may not suit everyone's taste for that perfect sound.
I've spoken with a few avid racers and I was told to brush on a stripe of paint from the collectors up to the muffler inlets then look where bubbling starts and ends; supposedly, it give a general idea of the effective thermal area to work your components in, sounds reasonable to me. Since physics dictates that hot flows towards cold by nature, it makes sense to use that data and attach it to thermal velocity and scavenging low pressure.
Anyway, I wasn't looking to start a debate on who is the smartest on exhaust science, but, I was trying to evaluate some questions specific to the MGB layout such as:
1. How does the unique "short wheel base" of the MGB affects the rules of the design? It should be great help in scavenging exhaust and creating low pressure evacuation/filler aid?!?!
2. Are oval pipes helpful to under carriage room restriction?
3. Would an "X" or "H" pipe be affected by the short wheel base?
4. Would the stripe painting technique help create some basic blue print?
5. What advantages would result in mounting mufflers on each side of the fuel tank versus underneath the seat floor pans?
6. Has anyone experienced using different system on the MG and able to speak about noticeable trial and errors (do and don't)?
Well thought out fabrication is well spent money. I don't believe that the system has to be complex to deliver maximum performance, just well thought out. Guys, thanks a million for your input, it helps tremendously in asserting a plan.
Ground clearance will always be a problem with any MG set up for fast cornering and hard driving. The mufflers and pipes will always hit first so anything that can be done to increase clearance there will help. Also, shorter pipes do not need to be as large in diameter as longer ones so for instance, using 2-1/4" instead of 2-1/2" pipe buys you extra clearance, as does tucking the pipes in closely. Remember, even the 2-1/4" is significantly larger than original and leaves less ground clearance. This was the stimulus behind the exhaust system on my roadster, which never extends below the body and therefore gives maximum ground clearance. I simply couldn't keep an exhaust system on the car before going to that system and was constantly grounding the pipes. However, most cars don't sit that low so it isn't quite as much of a problem. It is still a concern with speed bumps and such though. Oval pipes are fine for a straight run but I think you'll run into trouble with bends. For mufflers I'd try turbo mufflers under the car and smaller glass packs beside the tank. I think that will give a good balance with minimal back pressure. Use the thinnest turbo mufflers available underneath and center the tank. Then if you don't care for the sound it's fairly easy to modify it. We went with rear glass packs only (or they might be baffled bullet mufflers) on the MG-Roadmaster and it sounds good and that does give extra ground clearance, but might get a bit loud over time. It's a low compression engine though and a high compression engine will have a sharper and louder sound. An "H" pipe is worth doing but I'm not sure I've ever seen one on an MGB. Again, crossing under the frame rails cuts ground clearance and this is at a spot that is likely to ground anyway. I've considered a crossover but never have designed one for just that reason.
JB
Thanks Jim, after reading your postings for 2-3 years now, I sense that no one puts as much time in R & D as you do; that alone should crown you as "The Go To Guy".
Where do you find the time?
Jacques
I'm an insomniac ;-)
JB
@ California Kid
Take a look at SpinTech's "Cruiser" mufflers. That's what I'm using on my Healey. Only 2 1/4" tall and supposed to be relatively quiet. I was looking for a system that would give me the most ground clearance for the Healey and the only way I could think of something that might give me more than the Cruisers were chambered pipes like on Dan Master's MGB-GT, but I think they would be louder than the SpinTechs. Haven't got the exhaust on yet, so don't know what the ultimate sound would be like. Sanderson makes some block huggers for SBF's that might work for you, but I've read some people aren't too happy with their quality: http://www.sandersonheaders.com/Sanderson-FF1-Small-Block-Ford-Blockhugger-Header-Set.html
HealeyRick,
Thanks for the tip. The SpinTech product's "oval" tubing is an interesting option.
I didn't see any detail on the make up of the SpinTech mufflers (will be going back to look again)... I really like what I've heard about the DynoMax Super Turbo's design and function - David Vizard (http://www.amazon.com/David-Vizard/e/B001JOWD4M) was instrumental in the original design - apparently often copied by others.
I have looked at the Sanderson headers. I have not heard anything about the quality, but the gasketless design gives me concern.
There are some other headers that are not exactly center-dump that might work, and alot of the center-dump headers look like they would dump right into the frame rails... Might have to go 'custom' to properly fit...
Thanks again for the post.
Mark
Hey Jacques,
I was just using the gas miser example to show a tuning route that some might be interested in. I think if you re read my post you'll realize that I discounted that option in your situation. Mpg in your case is going to end up where ever it ends up, which should be pretty good with the correct gearing.
Your friends Vette aught to get excellent hwy. mileage. It's engine management and engine design are light years ahead of the SBF stuff. Add to that an overdrive ratio that puts the engine just off idle at cruising speed and you have a winner.
Use caution with your rocker ratios. Everything changes with the ratios and not always the way you would expect. In general a ratio change is used when the cam choice is limited. The duration of your cam stays the same with a ratio change. The lift and valve acceleration change and often overstress the valve springs. Modern cams are designed around specific rocker ratios and tend to under perform when this is changed. If you are looking for a certain performance level then chose a cam that meets it and you'll be much better off. Changing your cam timing doesn't get you any more power ( unless it was grossly out of time in the first place). What it does do is allow you to move the torque peak around. Advancing the cam pulls the torque peak back some to a lower rpm level and retarding it moves it up. Once again care needs to be exersized here.Like the ratio change it alters the piston to valve clearance and if overdone can send your exhaust temp through the roof.
I still think that the 2-1/4" system is your best bet for several reasons. #1 is ground clearance #2 is it will support your HP level well.#3 is exhaust velocity and #4 is ground clearance.
A 2-1/2" system has bragging rights but it won't make your car any faster.
Take the "Turbo muffler" thing with a grain of salt. Some are very good and some are not. Legend has it that the turbo muffler started out on the old Corvair turbo. GM found that the turbo muffled the car so much that a full blown muffler was no longer required. Street racers found that this new muffler with fewer internals sounded good and went better than the mufflers of the day. Thus the "Turbo Muffler" moniker. Reality was that they were terrible by todays standards but the name lives on. Choose your muffler by flow level and sound quality not marketing hype.
The paint stripe on the pipe is a time honored tuning tool and it works well. Build your system without mufflers or crossovers and paint it with the cheapest stuff you can find. Check for cops and take it out for a hot lap around the block. You're going to find the paint burnt within a foot or two of the collector. Your crossover goes here. Install the crossover then drive it like you stole it again. The hot spot after the cross over is where the resonators go. Use a resonator with a greater volume than your pipes and the system will think it ends there. After that put your mufflers wherever you wish and your done.
The reason for the hot spots is due to harmonics and resonance. The pipes get hotter wherever two exh pulses collide. The out going pulse meets a returning one. This effectively becomes a restriction and you want to provide a release for that pressure. As you can see wheelbase doesn't really enter the picture.
I think the spin tech pipes are a great. Use them where the clearance is minimal then use the adapters to round them up for better muffler choices.
Thats all I've got for now.
Cheers
Fred
"I don't know everything that works......but I know an awfull lot about what doesn't".
Fred,
Your guidance to Jacques on the paint trick is superb! Makes complete sense! You also confirmed most of my understandings to date - your rationale for 'H' or 'X' pipe location give better justification than I had found elsewhere.
Following is a good explanation of some of the peculiarities of V8 exhaust design I found: "Experience indicates inline four-cylinder engines are more sensitive to primary pipe length, but a two-plane cranked V-8 is not two inline fours lumped together. It is two V-4s and, as such, does not have even exhaust pulses along each bank. With a conventional, as opposed to a 180-degree header, exhaust pulses are spaced 90, 180, 270, 180, 90 and so on. The two cylinders discharging only 90 degrees apart are seen, by the collector, as one larger cylinder and accounts for the typical rumble a V-8 is known for. This means the primaries act like they do on a four-cylinder engine, but the collector acts as if it were on a 3-cylinder engine having different sized cylinders turning at less revs. (Doesn't life get complicated?) This, plus the varied spacing between the pulses appears to be the cause of the system's reduced sensitivity to primary length..." courtesy of David Vizard from an article published in February 2009 in Super Chevy titled "Exhaust Science Demystified."
http://www.superchevy.com/technical/engines_drivetrain/exhaust/0505phr_exh/index1.html
Re. validation of using an 'H' or 'X' pipe, because of the unbalanced pressure caused by the peculiarities of V8s noted above (i.e. the "3-cylinder engine having different sized cylinders"), "Virtually all V-8 exhaust systems can be refined by the addition of a balance or X-pipe. These have two potential attributes: increased power and reduced noise. Extensive dyno testing on both of these factors has indicated balance and X-pipes are 100 percent successful at reducing noise. The reductions amount to a minimum of 1 dB to a maximum of 3 dB with 2 dB being common. As far as power is concerned, things are a little less certain. With engines between about 325 to 550 hp, experience indicates that in about 60 percent of the cases (mostly with balance pipes), the engine can deliver as much as 12 additional hp, with 5-8 being the most common. The other remaining 40 percent tested showed virtually no change in output either up or down. Based on such results, we can conclude that a balance or X-pipe is always a positive asset and never a negative..." again courtesy of David Vizard's article.
The choice between a balance ('H') pipe and an 'X' pipe is a little more personal, but some analysis has been done in less than scientific manners that lean twoards 'X' pipes being both quieter and more productive.
See: http://www.boyleworks.com/ta400/psp/exhaust.html
Also note that the system design suggested by David Vizard in the referenced article incorporates a large resonator box that is also basicly just a large 'X' pipe...
You may not have given me the math I was hoping for, but you certainly gave me a map to follow...!
Thanks!
Cheers,
Mark
> I have been reading, and working (above my head) with all sort of
> calculations,
The formulas are a starting place but the wave dynamics are complex enough
that dynamic simulation is required. David Vizard wrote an excellent exhaust
system article "Exhaust Science Demystified" that was published in the May
2005 issue of Popular Hot Rodding and another good article "No Loss Exhaust"
that was published in Drag Race Monthly. In these articles, Vizard gives some
design criteria for header and muffler sizing. The equations are based what
the exhaust port flows at your maximum exhaust valve lift and apply to bank
separated 4-into-1 headers on a V8. I use his equations as starting points
for Dynomation iterative simulations so I wrote a little routine to calculate
the parameters. It's in Fortran and I've cut out the relevant section below.
For a SBF, treat the calculated collector length as a minimum value for best
performance. The SBF typically responds to long collector length (helps
increase velocity in the short exhaust port), regardless of cam or RPM. Long
in this context is up to 24 inches. The Flowmaster 4-2-1 collectors work well.
The optimum collector length is best determined by testing but there will
typically be a noticeable burn pattern inside the collector which will indicate
the length the engine wants. The primary diameter should be based upon what
the exhaust port flows and is typically a bit larger than the exhaust valve
diameter.
C Calculate exhaust parameters (initial values for Dynomation)
C
C OID = optimal internal diamter (inches)
C Ex_CFM = exhaust port flow (CFM) at 28" H20 (peak within max valve lift)
C FD = flow density (around 80 CFM/square inch @ 28" H20)
C CDiam = collector diameter (inches)
C
C Based upon Vizard articles:
C "No Loss Exhaust", Drag Race Monthly (date?)
C "Exhaust Science Demystified", May 2005, Popular Hot Rodding
C
C Primary lengths should fall between 24 to 36 inches (for bank separated
C 4-into-1 headers on V8's with dual plane crankshafts)
C Collector length between 12 and 20 inches suitable for up to 8000 RPM
C Mufflers should flow 2.2+ CFM per HP (the point at which there is a
C 1% difference between mufflers and open pipes), e.g. 500 HP requires
C two 550 CFM mufflers
ELSEIF (OPT .EQ. 11.0 ) THEN
WRITE(*,*) 'Horsepower Goal:'
READ(*,*) HP
WRITE(*,*) 'Peak Exh Flow in CFM at 28" Hg within max cam lift:'
READ(*,*) Ex_CFM
FD = 80.0
MFLOW = 2.2 * HP
OID = SQRT (Ex_CFM * 1.27/FD)
CDiam = 1.75 * OID
WRITE(*,*) 'HP Goal =', HP
WRITE(*,*) 'Exhaust Flow =', Ex_CFM
WRITE(*,*) 'Required Muffler Flow =', MFlow
WRITE(*,*) 'Primary ID (inches) =', OID
WRITE(*,*) 'Collector ID (inches) =', CDiam
WRITE(*,*) 'Primary lengths between 24 to 36 inches'
WRITE(*,*) 'for bank separated 4-into-1 headers on'
WRITE(*,*) 'V8s with dual plane crankshafts)'
WRITE(*,*) 'Collector length 12 and 20 inches good to 8000 RPM'
> to formulate the perfect exhaust system for my MGB powered by a
> Ford small block (331) stroker.
I'm working on a couple of small block Ford (SBF) engines at the moment.
One's an EFI 5.0L with AFR 165 cylinder heads, the other a carburated 331
with Floo Tek heads (Australian castings, assembled in Indy).
> Having said that, the reality is that having the wrong mufflers or pipe
> size can defeat the perfect induction system.
Stock exhaust systems can be very restrictive and mufflers are absolutely
critical. I recently dyno tested three different ANSA mufflers on a 400
to 525+ HP 351C Ford V8's, along with stock exhaust manifolds and several
sets of heads. The ANSA mufflers lost over 50 HP compared to Magnaflow
stainless steel mufflers. The Magnaflow mufflers were within a couple of
HP of open pipes. We gutted the ANSA mufflers and they still lost 38 HP.
> By contrast, the old and poorly appreciated cast iron log manifold,
> precisely because it is incapable of being tuned to a precise range, gives
> a very flat performance curve which, it turns out is just what you usually
> want in an average passenger car.
I've got to disagree here. Headers are among the best bang-for-the-buck
modifications for a SBF, increasing power across the rev range. Even on
an engine like the 351C-4V which has cast iron manifolds with large passages,
the effect is quite dramatic. When we tested cast iron manifolds against
long tube headers, the headers were better across the rev range. At the
peaks, the OEM cast iron exhaust manifolds were down 34 HP and over 38 ft-lbs
of torque compared to the headers. In the 4000 RPM range, the manifolds cost
50 HP and the idle was noticeably worse. Bottom line is you can lose a bunch
of power on a poor mufflers and cast iron manifolds. The best mufflers for
performance are the straight through designs. The better ones use stainless
steel packing that doesn't burn out like the fiberglass stuff. Some of the
muffler companies are flow rating their mufflers now. To be non-restrictive,
mufflers should flow 2.2+ CFM per HP (the point at which there is a 1%
difference between mufflers and open pipes). For instance, 300 HP requires
two 330 CFM mufflers. Cross over pipes near the collectors can help with both
power and noise. Cams with narrow lobe centers are more sensitive to back-
pressure and require good mufflers to work properly.
> BTW, maintaining back pressure turns out to be a myth, it has nothing to do
> with fine tuning exhaust formulas.
Yes, that myth dies hard. While racers do add header collector extensions,
it's not to increase backpressure. They do it to alter the acoustic tuning.
> Back to the dirt bike, these engines are renowned for a peaky powerband, primarily
> because the pipe is tuned to provide the greatest possible suction volume at the
> exhaust port at a particular rpm, known as being "on the pipe" and they create
> tremendous power at that engine speed, but can be absolute dogs below that.
> This would be bad in a street driven car.
This pronounced effect is specific to 2 stroke engines and does not necessarily
transfer to 4 stroke engines like a SBF.
> The crossover pipe seeks to even out the exhaust pulses
On an engine with back pressure, the primary effect of a cross-over pipe is to
permit sharing of muffler flow, increasing the effective flow rate of the
mufflers.
> From the '70s muscle cars it was very clear that upwards of 300 hp was easily
> supported by a header down pipe size of 2-1/4" and a 2" tailpipe, and in fact
> this was almost the standard.
Going from a larger down-pipe to a smaller tail pipe is a power killer.
It's nearly always better to step up to a larger muffler and tail pipe size.
> The point being that bigger pipes can be used if desired and may help produce
> more peak power, but could potentially narrow the torque band a bit.
The collector outlet diameter is key here. For a wide power band, don't use
too large a collector.
> At the same time, the exhaust system as a whole will have one resonant frequency
> where it is most efficient.
But there will be subharmonics as well so the effect is not only at a single RPM.
> You mention racing tuning, street manners and mpg. It's like the old saying, you
> can have your car "good" "fast" and "cheap" pick any two.
A well coordinated engine can provide a large increase in power with only a small
decrease in cruise fuel economy. I recently designed an engine for a friend's
Pantera. His poorly coordinated prior engine made We went from under 300 HP to
526 HP and he now gets better gas mileage (at least when he keeps his foot out of
it). Though it's an oldie, David Vizard's Performance with Economy book is still
recommended.
> Tuning for mpg is a very interesting subject and while optimizing the drivetrains
> efficiencies is the path to greater hp I don't think you built a 331 to be a gas
> miser.
Getting good fuel economy on the highway is about low drag, minimum cam overlap,
high (dynamic) compression and tall gearing. Running the engine well below peak
torque at cruise (via tall gearing) helps fuel economy because you need a larger
throttle opening for the same power which reduces throttling losses which, in
turn, means lower BSFC. Ideally, you'd run at near WOT at cruise (with any sort
of power enrichment disabled and timing optimized) but acceleration would be very
sluggish and you'd need to change gears just to accelerate or run up hills. Lower
RPM also leaves more time for complete combustion.
The new Corvette Z06 is an example of what can be done these days. It makes 505
net HP yet still meets emissions goals and is rated at 26 MPG highway. The Z06
has relatively low drag, a short duration hydraulic roller cam (211/230 degrees
duration, 0.591" lift), high compression (11:1) and very tall gearing (in sixth
gear). The result is good highway fuel economy even though the displacement is
427 cubic inches (7 liters). The large displacement and minimal overlap means
lots of torque which allows the engine to cruise at low RPM yet still have plenty
of power to pass without down-shifting. The lightweight valvetrain, high cam
lift, and excellent cylinder heads (360 CFM intake at max lift) allow it to make
excellent power. The 400 HP LS2 in the base model Vette is rated at 28 MPG
highway and many owners report pulling 30 MPG on the highway.
> In the real world,not the magazine Disneyland, a really good two valve 331 might
> get 350 hp on a good day.
While I agree that magazine numbers often inflated (David Vizard and Rick Anderson
are two builders that publish honest numbers), a good 331 can make considerably
more than 350 HP but it requires really good cylinder heads.
> (We really should be talking torque but hp is so much cooler)
A discussion for another post. For now, allow me to suggest what you want to
design for is the maximum average power between shift points.
> I don't want to cause trouble but, Flowmasters flow like @#$%&.
and are sensitive to distance from the collector.
> Dynomax turbos flow very well and Magnaflows sound awesome.
Magnaflows work very well.
> Also employing a 331 SBF like Jacques...
> On the dyno, my engine peaked at 400 bhp @ 5800 rpm / 416 lb-ft @ 4200 rpm.
> Report starts at 2800 where it was 375 lb-ft and 200 bhp, and closed out at
> 6000 with 350 lb-ft and 398 bhp. Has a forged steel crank, forged pistons,
> Edelbrock aluminum heads and intake, a tuned 'Stage 2' Holley 650, a 'mild'
> Comp Cams Hydraulic Roller Cam kit
Which version of the Edelbrock heads?
> From what I've read in notes by David Vizard (a guru), header tuning isn't that
> important on a street bound V8 (where this will live - hell this thing is going
> to have AC...) - his reference engine for what I read was the Chevy 350.
What? Vizard is a strong proponent of headers on street 350's with plenty of
dyno testing to back it up. Perhaps you're confusing equal primary lengths.
Vizard has shown that bank separated 4-into-1 headers are insensitive to
relatively large primary length variations. 180 degree headers are very sensitive
to equal primary lengths. On a 90 degree V8 with 2 plane crankshaft, 4-into-1 bank
separated headers are much less sensitive and are able to tolerate large variations
in primary length. Much more important than equal length is the radius of the bends.
On a SBF, the collector is more important than the primary length. The mufflers are
as important as the headers.
> I've read about really quiet 'three-muffler' systems used on big Turbo-Buick
> 10 second dragsters that are so quiet you can barely tell the engine is running
Turbos tend to quiet down exhaust all by themsleves.
A Helmholz resonator can be used to tune specific frequencies but absorptive
media works over a wider range. Lots of small holes in the tubes, surrounded
by the absorptive media. More volume makes it easier. More cylinders raises
the frequency and that diminishes the size of the elements required. Large
volume can smooth out pressure waves. The pressure waves can excite vibrations
in the shell of the muffler and cause it to radiate noise. That's why shells
are nearly always round or oval and are often double wrapped for damping.
For Panteras which have dual tipped muflers, we've made removeable inserts
to quiet them down on trips.
> Thinking of starting with 2 1/4 pipe from the headers back and running 2 inches out
> from the mufflers to some sort of shiny tips...
I would not reduce the diameter at the tail pipe. Stay the same or larger.
However, we have made removeable inserts to quiet down loud exhaust on trips.
> I'm using the old reliable Ford Racing E-303 bump stick in EFI form.
> I've installed a full roller rocker with a 1.72 ratio
For nearly all aftermarket heads, the E-303 will work better if you run 1.72:1
rockers on the intake side and 1.6:1 on the exhaust. I've personally tested
this and the effect is even stronger on dual pattern cams. What EFI intake
manifold are you using? If you are running one of the long runner EFI intakes,
that will drive much of the tuning considerations. Make sure your springs are
strong enough to handle the E-303 and 1.72:1 rocker ratio.
> Again, with assumptions based on engine improvements, 2-1/2" piping is within
> the rules of given specs.
2 1/2" duals all the way back will work fine as far as the engine is concerned.
I have no experience with what fits in the MGB but you want a long collector.
Sacrifice the primary length if you must to get the desired collector length.
The larger the pipe size, the harder it is to make the bend over the rear axle
and still clear everything. It's okay to increase pipe size as you go aft but
you do not want to have larger pipes dump into smaller ones as you go aft.
What cylinder heads are you using?
> The duration of your cam stays the same with a ratio change.
While the duration of the lifter stays constant, the duration at given valve lift
(and the period of overlap) changes. The effect is relatively small, however.
Dan Jones
Excellent reply Dan,
I was heading to my library to get Mark some recommendations for his "math". But you beat me to it.
Like you, I strongly recommend anything that Vizard has written as mandatory reading.
Another good reference is Scientific Design of Exhaust and Intake Systems by Phillip Smith and John Morrison.
The book is a little dated (at least mine is) but physics don't really change over time.
Cheers
Fred
Wow, lots of Vizard fans here. Used his Mini books on the A Series BMC engine as a bible when building my bugeye. David does a weekend seminar for $550. I'd bet this would be a huge bargain for pro motor builders:
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http://www.davidvizardseminars.com/
Dan,
Wow....
First things first, my apologies - I over simplified my statement re. headers. You were absolutely correct in assuming I was referring to equality of primary lengths - or rather the 'lack-of-the-necessity-of' equality for my application / non-180-degree 4-into-1 split system...
I've noted that secondary length is important (seen 18" to 24" as good rule of thumb)... but your note is the first I've seen keying in on collector dimension importance for the SBF. Am I making a mistake in nomenclature - in this discussion are you using collectors and secondaries interchangeably? If not, what guidance can you give on collector dimensions?
The Edelbrock heads I'm using are the Performer RPM - 1.6 inch exhaust valve / recommended 1500 to 6500 rpm range:
http://www.edelbrock.com/automotive_new/mc/cylheads/ford/sb_perf_rpm.shtml
Having a hard time finding commercial headers for the SBF that have primaries of larger diameter than 1.6" and will fit my car (short / center dump / non-block hugger - need to clear 23" outside width of frame rails / 1958 AH 100-6 on a custom Jule Enterprises frame).
I'm assuming I should be going with headers with 1 5/8" ID primaries because of the heads I'm using... I expect the primaries should be ~18" long and lead to 4-into-1 collectors with conventional 2.5" ID terminations that will be plumbed down to ~24" long 2 1/4" ID secondaries leading to a 3" ID resonator (maybe a Dynomax 'X' pipe / killing two birds with one stone / expansion to 3" used to tune length of secondaries) before plumbing to a pair of Dynomax Super Turbo mufflers (or comparable) that flow ~440 cfm each. I will likely follow your recommendatin and not skinny down the exhaust to 2" after the mufflers as was previously considered.
Afraid I might be going custom on yet another aspect of this project for the headers... In that event, you noted that bend radiuses are important - any specific guidance assuming 1 5/8" ID tube?
And Dan, thanks for your thorough and thoughtful post... You obviously know your stuff...
Cheers,
Mark
Thanks for the very informative post Dan. It's good to get some of the mysteries of exhaust tuning cleared up a bit, and we all know there is plenty of mystery about it. So how about another question? Could you elaborate on that business about not stepping the pipe size down after the muffler? That's a trick the manufacturers have used pretty much forever and are still doing so there must be some pretty good reasons for it. Seems like if it was that much of a power killer it would have disappeared a long time ago. (Of course we might say that manufacturers aren't interested very much in performance but I don't really believe that. Maybe it's because I'm not trying to find that razor's edge of maximum performance either.)
Another thing worth mentioning is that extremely few of the headers used in LBCs are equal length headers, which means a great deal of the effectiveness of having headers is lost right there. In fact, as bad as cast exhaust manifolds are, some well executed designs are out there which perform as well as some of the minimalist shorty tube headers. So it's really more a question of degree and of quality of execution I think. And here is where the advantage lies in building your own headers. As an example, I built headers for my 215/MGB roadster 25 years ago using guidance and parts from Ed (Headers by ED) and built true equal length primaries +- 1/8". The performance of those headers has been exceptional, but fitting them into an MGB was a challenge. The good news is that they are good enough that I'll still be able to use them on the 340 that is going in the car now. At 1-3/8" x 34" on the primaries the tubes are only a smidgen larger than the exhaust valves and at 2-3/8" the collector could be a bit larger without hurting anything but it will work just fine. The set was sized for a 5L displacement so it was a bit big for the 215, and a bit small for the 340 but close enough. And it keeps me from having to build another set. Considering that I had 80 hours of construction time invested, I consider that a very good compromise.
There are probably more compromises in a car's exhaust system than in any other part of the vehicle, at least for a passenger car and especially a LBC. Header primary size certainly can be in that category. Fitting all those tubes in is difficult enough at 1-3/8", if they had been 1-5/8" I don't think it would have been possible without very major redesign of the car's monocoque structure, or else seriously compromising on primary tube length. Choosing between equal length tubes and a step down in tube size, I think the advantage goes to the smaller equal length tubes. Maybe Dan can prove me wrong on that one.
Finally, although I don't really see the relevance of the information about 180* headers it's good to know and interesting from an engineering perspective. Since it is such a plumbing nightmare even in an open chassis race car though, not much of that applies to LBCs. In a practical sense we're pretty limited on where and how the pieces can be fit together and often performance considerations have to give way to practicality.
JB
> Wow, lots of Vizard fans here.
Yup. Vizard turned me on to Dynomation.
> I've noted that secondary length is important (seen 18" to 24" as good rule
> of thumb)... but your note is the first I've seen keying in on collector
> dimension importance for the SBF. Am I making a mistake in nomenclature - in
> this discussion are you using collectors and secondaries interchangeably?
Secondaries typically apply to tri-y headers where you have a primary length
(applies to 4 tubes) which then merge into two short collectors, followed
by two secondaries which then merge into a single collector. The collector
length I refer to is specific to V8 headers where all four tubes (per side)
go into a single collector. To further complicate matters, there are various
styles of collectors including tri-y collectors. The Flowmaster 4-2-1
collectors are of this type. I refer to pipes aft of the collector as
intermediate pipes and pipes after the muffler as tail pipes.
> If not, what guidance can you give on collector dimensions?
> The Edelbrock heads I'm using are the Performer RPM - 1.6 inch exhaust
> valve / recommended 1500 to 6500 rpm range:
See Vizard's equations above and my recommendations specific to SBF V8's.
Unported Performer RPM heads flow around 175 CFM @ 0.500" lift and 180 CFM
@ 0.550" lift. Assume a 400 HP goal.
1.66" primary diameter
primary length of between 24 and 36 inches
collector diameter of 2.91"
collector length of 20 to 24 inches
dual mufflers of 440 CFM flow
The flow bench numbers above are with a pipe stub so are optimistic for our
purposes and the exhaust port blows down early in the lift cycle so use a
slightly smaller primary diameter. As a starting point in my Dynomation
simulations, I'd use:
1 5/8" = 1.625" primary diameter
3" collector (I'd prefer 2.75" but not many commercially available)
20 to 24 inch collector length
2 1/4" intermediate pipes leading to 2.5" inlet Magnaflow mufflers
Commercially available SBF 5.0L headers typically have primary lengths between
28 and 31 inches long. Hedman makes 1 1/2 to 1 5/8 step 4-into-1 full length
for both classic and Fox body Mustangs. There are also tri-y designs which
might package more conviently.
> Having a hard time finding commercial headers for the SBF that have primaries
> of larger diameter than 1.6" and will fit my car (short / center dump /
> non-block hugger - need to clear 23" outside width of frame rails / 1958 AH
> 100-6 on a custom Jule Enterprises frame).
Most long tube SBF headers fall into early Ford/Mustang designs which turn
down sharply at the exhaust port to clear the narrow shock towers or later
Fox body Mustang headers which are designed for a more generous engine
compartment. There are also a variety of race, swap and street rod headers.
The only center dump designs I've seen were street rod block huggers.
> I'm assuming I should be going with headers with 1 5/8" ID primaries because
> of the heads I'm using... I expect the primaries should be ~18" long and lead
> to 4-into-1 collectors with conventional 2.5" ID terminations that will be
> plumbed down to ~24" long 2 1/4" ID secondaries leading to a 3" ID resonator
> (maybe a Dynomax 'X' pipe / killing two birds with one stone / expansion to 3"
> used to tune length of secondaries) before plumbing to a pair of Dynomax Super
> Turbo mufflers (or comparable) that flow ~440 cfm each. I will likely follow
> your recommendatin and not skinny down the exhaust to 2" after the mufflers as
> was previously considered.
See above for my recommendations.
> Afraid I might be going custom on yet another aspect of this project for the
> headers... In that event, you noted that bend radiuses are important - any
> specific guidance assuming 1 5/8" ID tube?
Not really. The chassis usually dictates the bends.
Dan Jones
This is an outstanding thread!
One sub-topic I'd like to see discussed in a little more depth is optimization of tri-y headers for a V8. Which of the 4-into-1 rules of thumb apply, and which ones don't? Is it true that the diameter of tri-y primaries can reasonably be smaller? Sized to match intake port size? How long should they be? I'm thinking of building a set one day for a Rover 4L motor.
Dan,
You pretty much mapped it all out there didn't you...
Thank you so very much!
I loved reading that your modeling software was written in Fortran. I learned to code in Basic, Cobol, Fortran and Pascal my freshman year of college - 28 years ago!
If you need a hand buying or selling a company (Internet media has been my specialty of late), give me a ping and I'll be happy to give you some advice!
Martin Jansen of Jule Enterprises, the party building my car for me, asked me if he could start photographing my car as it comes together and posting the pictures on his site for other 'modified-Healey' guys to see. I told him I'd love it. So if you are interested in how your guidance gets applied you should go to Martin's site and look for my car in a while (Jule Enterprises is listed as a sponsor of BritishV8 - I expect the moderator won't mind the plug).
Thanks again Dan! Your knowledge is obviously deep, and your advice worth heeding. Best of luck with your many projects.
Cheers,
Mark
Dan, not to take anything away from other replies, but you appear to be the one that excels on this subject. I feel like some poor guy showing up to a gun fight with a knife (LOL).
From the beginning of this MGB project, I proceeded with a plan based on personal experiences, member's feedbacks and wishing like heck that my approach later would not result in major adjustments and redo. You asserted some of my choices based on similar rationales, except that my choices were based more on wishful deductions.
I'm now 58 years old and semi-retired; during my career as a mechanic I've worked more as a repair technician in a large automotive fleet. Our company sent us to seminars and training through Ford, GM and Chrysler. Basics and fundamentals were learned based on street vehicle to address its preventive maintenance, repairs and components overhaul based on factory specifications and procedures.
Hot rodding modification has always been a weekend interest of mine, again, based on factory high performance vehicles. During my younger years, there were a lot of "snake oil" products purchased with great disappointment. What I'm trying to say is that unless you are a seasoned race mechanic that understands in depth fundamentals to all out performance, and, that has extensively worked to acquire a winning edge, than, the rest of us have to look for these "Guru" out there.
I'll answer some of your questions concerning my 331 FSB heads and intake choices; when I started the engine build up consideration, I decided to give a call to "Air Flow Research". I've explained to them that I wanted to build the car mostly for joy ridding to include an occasional fun street fight. First question asked, was what camshaft selection was used; since I already had purchase the Ford Racing, roller E-303, they recommended the AFR 165 heads with Scorpion 1.72 roller rockers. Only later did I decide to go with a stroker kit. I've called them back to ask if the heads and matching components were still adequate, they asserted that the "low end" torque would be pleasing with the way their heads flow and the new combo.
It was AFR that suggested using a 1-5/8" primary tube and 2-1/2" pipes. They indicated that because I was using the Ford Racing GT-40 EFI intake and the AFR 165 smaller valves (1.60 and 1.95) were going to create real nice air velocity. The rest of the engine is all 4340 forged steel. A 65 MM throttle body and 24 pounds injectors finish off the induction side. An aluminum flywheel was added since plenty torque allowed a trade off between inertia and quick revving.
All the same questions were asked concerning, horsepower, torque, and how could fuel efficiency find a spot by addressing good EFI management. It has a new Summit Racing T-5 with a tall OD, tires are P205/60VR15 and the differential ratio stands at 3:42.
Last but least, is the exhaust tuning to work in harmony with the above and that is why I started this thread. So far, because of the stellar answers given, I have a pretty good grip on how to proceed. If it wasn't for of all you accomplished performance members, I don't think that anyone could find answers in a factory repair manual.
I forgot to attach the link to my AFR 165 heads; it has awesome flow numbers for up to 331 cubic inches: http://www.airflowresearch.com/index.php?cPath=21_23
Jacques
> One sub-topic I'd like to see discussed in a little more depth is
> optimization of tri-y headers for a V8.
Unfortunately, my simulation program doesn't have an option for tri-y
designs. Vizard's dyno testing experience suggests they work well for
relatively mild cam timing (under 270 degrees seat duration) and are
relatively insensitive to length. He suggests the primary/secondary
split be on the order of 1/3rd to 2/3rd the overall length. There's
a header sizing program called PipeMax that supposedly does tri-y's
well. I've been meaning to look into that one of these days.
> Which of the 4-into-1 rules of thumb apply
> Is it true that the diameter of tri-y primaries can reasonably be
> smaller?
I'd still use the primary pipe sizing from above. That needs to match
the exhaust port flow capability (within the cam lift limits). After
the first merge, I'd step up a size.
> Sized to match intake port size?
They should be sized to the exhaust port size. The intake side is
larger because the exhaust is under higher cylinder pressure while
the intake side see only atmospheric pressure.
> You pretty much mapped it all out there didn't you...
Remember, those are just my starting points (and rationality checks) for
iterative Dynomation simulations but should be pretty close.
> I loved reading that your modeling software was written in Fortran.
> I learned to code in Basic, Cobol, Fortran and Pascal my freshman year of
> college - 28 years ago!
Sounds like we were in college taking programming around the same time,
though I actually was introduced to Fortran while in high school.
> If you need a hand buying or selling a company (Internet media has been my
> specialty of late), give me a ping and I'll be happy to give you some advice!
Thanks!
> So if you are interested in how your guidance gets applied you should
> go to Martin's site and look for my car in a while (Jule Enterprises is
> listed as a sponsor of BritishV8 - I expect the moderator won't mind the
> plug).
Cool, I'll watch for it.
> During my younger years, there were a lot of "snake oil" products purchased
> with great disappointment.
That's a motivating factor for me, trying to help others avoid mistakes
I and friends have made along the way. Back then, before the internet,
we had to work for every drop of information now it's forced through a
firehose and the problem is sorting out fact from fallacy.
> since I already had purchase the Ford Racing, roller E-303, they recommended
> the AFR 165 heads with Scorpion 1.72 roller rockers.
I'm using AFR 165 heads on my own '87 Mustang GT with plans to add a Novi 1000
supercharger. You'll probably want AFR's upgrade springs with the larger
rocker arm ratio.
> Only later did I decide to go with a stroker kit.
If you're using the 58cc AFR heads, you should be at around 10.4:1 compression,
closer to 10:1 with the larger chamber size. If using the SCAT kit, be aware
it is designed for a 28.2 oz-in balance factor. Your balance and flywheel need
to be designed for the same. If using a 5.0L roller block as your donor, be
aware it was 50 oz-in. Pre-'81 302's use a 28.2 oz-in balance weight, '81-up
5.0's are 50 oz-in, as are all 351W's and 351C's use 28.2 oz-in balance factors.
> I've called them back to ask if the heads and matching components were still
> adequate, they asserted that the "low end" torque would be pleasing with the
> way their heads flow and the new combo.
Yes. Those heads will work just fine with the cubes and other componenets.
> It was AFR that suggested using a 1-5/8" primary tube and 2-1/2" pipes.
Agreed.
> They indicated that because I was using the Ford Racing GT-40 EFI intake and
> the AFR 165 smaller valves (1.60 and 1.95) were going to create real nice air
> velocity.
True. You can pick up some power by porting the lower manifold of the GT40
intake set. It's cross-sectional area will be a limiting factor in your
build.
> The rest of the engine is all 4340 forged steel.
For a build like this, the weakest link are the two bolt main caps walking
around at high RPM. However, with the rev limiter of the EEC-IV and the
combination of parts, you won't be spinning it high enough where that will
be a problem. The Melling M-68HV's is a great SBF oil pump and it's worth
adding an FRPP Boss 302 windage tray. The Boss 302 windage tray works with
front sump pans and MPG Head Service has a similar part that works with
the Fox body double sump oil pans.
> 65 MM throttle body and 24 pounds injectors finish off the induction side.
I'd rather see 70mm and 30 lbs/hr injectors. You may be at the limits of
the injector flow rate, though that can be crutched with more fuel pressure.
> An aluminum flywheel was added since plenty torque allowed a trade off
> between inertia and quick revving.
Good move. You'll notice the difference, particularly in the lower gears.
I'm pretty sure I posted the analysis I did on the effect of running a
lighter flywheel.
> All the same questions were asked concerning, horsepower, torque, and how
> could fuel efficiency find a spot by addressing good EFI management. It has
> a new Summit Racing T-5 with a tall OD, tires are P205/60VR15 and the
> differential ratio stands at 3:42.
Traction will be a problem in lower gears.
> Last but least, is the exhaust tuning to work in harmony with the above
> and that is why I started this thread.
1 5/8" headers, 2 1/2" pipes and good mufflers should work just fine.
Most of the 1 5/8" primary diameter long tube headers will have a 3"
collector but a smaller 2.5" collector will usually make better power
overall.
Make sure you use a good timing chain. If your chain says Rolon (made
in India), do not use it. Be aware that most companies offering timing sets
do not make their timing sets. They repackage them from multiple vendors.
You need to know who made the sprockets and chains. One of the guys on the
FE board used to work at Speed Pro. When he worked there they had a bunch
of offshore companies trying to be suppliers, so they piggybacked some chain
and sprocket testing on an OE bearing durability dyno run. The Rolon chain
from India cost them the test motor a couple times when it failed before the
test was completed. A summary of the test results for the chains is listed
below. Speed Pro ended up using Dynagear sprockets and Morse chain but had
some quality control issues then Dynagear went out of business. After that
they sourced the high end Cloyes sets (which used high quality Renold and
Iwis chain) and the quality control complaints went away. The Ford Motorsport
timing sets I've purchased have used the Renold or Iwis chain and I've used
some of the higher end Comp Cams sets which used Cloyes. The sprockets come
from Rollmaster (Australia), SA Gear (US but poor quality) and Cloyes (US,
not pretty but good quality). Avon also makes some sprockets but sources
others. Dynagear (US) used to make sprockets but went out of business.
A bunch of the performance aftermarket companies are selling poor quality
chain from India (Rolon), along with sprockets from Australia (Rollmaster,
J.P Performance) or SA gear.
Chain durability testing summary:
Iwis (German) - looks very nice but was not tested, but has excellent
reputation as an OE supplier, used in high end Rollmaster
and some high end Cloyes sets
Cloyes (US) - tested OK
Renold (France) - tested excellent, used in most high end Cloyes sets but not
always
Morse (US and Mexico) - tested excellent
Daido (Japan) - tested excellent
Tsubaki (Japan) - tested excellent
KCM (Japan) - looks very nice but was not tested
Rolon (India) - failed test
Sprockets:
Rollmaster - Aus - pretty - never examined QA, good reputation
SA Gear - US - ugly - crappy
Cloyes - US - not pretty - good QA
Dynagear - US - out of business - so-so when they existed
Avon - some sprockets, buys everything else
Crane - buys everything
Comp - buys everything
Speed-Pro - buys everything
Ebrock - buys everything
Melling - buys everything
Elgin - buys everything
Note: Some of the test data was from Speed Pro, other from TRW.
The high end Cloyes and Ford Motorsport stuff tends to use the Renold chain
but the lower end Cloyes may use inferior chain. Rollmaster usually uses
Iwis chain which is top notch. I picked up an Australian Muscle Parts set,
thinking it was a Rollmaster but it turned out to have the inferior Rolon
chain from India.
> I forgot to attach the link to my AFR 165 heads; it has awesome flow numbers
> for up to 331 cubic inches: [www.airflowresearch.com]
I know them well and have a set sitting on my bench at the moment. The AFR's
cost a bit more due to the CNC runner and bowl porting but flow quite well
for the valve size. I ran your combo through Dynomation, assuming flat top
pistons, 58cc chambers for 10.4:1 compression ratio, long tube headers and a
GT-40 intake with ported lower and 70mm throttle body. The simulation predicts
around 385 HP. With an unported lower and 65mm throttle body, expect that to
drop into the 350 to 360 HP range.
Dan Jones
So, no further elaboration on the step down in tailpipe size I guess?
JB
> So, no further elaboration on the step down in tailpipe size I guess?
Vizard's testing has shown it to cost power to step down in pipe size
as it increases backpressure. Also most mufflers flow less than a
pipe of equal cross-sectional area so it's recommended for the muffler
to have at least the same ID and in many cases a step to a larger size
can help (e.g. 2 1/4" intermedaite tubes leading to a 2 1/2" inlet/outlet
tail pipe).
Dan Jones
Dan, thank you for your thoughts about tri-y headers. This thread is giving me the itch to fabricate something!
> Dan, thank you for your thoughts about tri-y headers. This thread
> is giving me the itch to fabricate something!
I'll be building and dynoing a 4.2L over the winter. Just got
the flow bench numbers back on the heads and designed the cam.
Should be good for 350 HP and be streetable. I've got a set
of small tube tri-y's, a set of Hedman 4-into-1 Range Rover
headers plus a box of headers tubes for something larger diameter.
If you bend up some headers, I can dyno them.
Dan Jones
Other than the "paint stripe", has anyone mentioned the "thermal factor"? I "suspect" OEM. reasoned smaller tailpies were an acceptable compromize, because of thermal losses ? Quite a bit of temp/pressure loss between point"A" and "Z" ? Production cars are a combo of thousands of compromizes. Almost always, the tailpipes must overpass the rear end.For this task, the smaller pipes are a fit. 2 cents, roverman.
Art, that was sort of my point, thank you. I suspect my post got lost at the tail of the last page, as Dan and I posted at nearly the same time. Similar to a production car, a street driven LBC has to have a lot of compromises, and where a big diameter exhaust system or a 180* header may be fine on other cars they will often be seen to create more problems than they cure here. Same as a cast manifold can be seen as part of the progression to an uncompromising set of headers, so too can the tailpipe size, and the best is not always the right choice. Equal length 1-5/8" primary, 3" collector headers in a lowered MGB are going to be quite challenging, and I'm not even convinced it can be done, at least not without a rock hard suspension, big cutouts in the fenderwells and you still might have a problem scraping the exhaust. If oversized tires have been fitted interference there is likely to also be a problem. The 2-1/2" or larger tailpipe is very likely going to have to go under the rear axle rather than over it and I suppose that's fine for all out performance but I did that once and won't do it again. You can't argue with test results and it'd be nice to know exactly what David's test setup was and what results, but common sense dictates that a cooler gas can use a smaller pipe and the temp drops hundreds of degrees from head to tailpipe. Also the empty spaces between the exhaust pulses are filled in as the slugs of exhaust gas are stretched out, making the pulses less dense which should also require less area for efficient flow. So one would think that the need for pipe area would diminish the further back you go. Again, referring to dirt bike systems, often the spark arrester is actually smaller than the head pipe. As for the 2-stroke being a totally different animal from the 4-stroke, well, not so much really. Both use the scavenging effect, both have overlap, both have pressure pulses and partial vacuum. The 2-stroke benefits from a partial pressure in the transfer ports (some do) and double the firing rate, but aside from that they are very much the same and for the most part the same principles apply. Very likely a 2-stroke style scavenger pipe would work just fine on a 4-stroke engine. I don't remember what the newer 4-stroke dirt bikes are running specifically, but I never noticed a difference in them when they first came out, and as an item of much curiosity I think a big change would have been seen and pointed out by someone at the time. Head pipes were smaller but that's all I remember.
So getting back to the cast manifold. Not to name names, but one very compact (but sleek) block hugger design which is popular can't be any more efficient than some of the factory cast manifolds we've seen. Looks much better and fills a distinct need, and it *is* a header, but in layout and tube size they aren't as good as the later model GM V8 cast iron manifolds for the LS1, and certainly no attempt at equal length tubes. So all I'm saying, it's a point in the spectrum. Where the all out race car needs to be and where the street driven LBC needs to be are worlds apart.
JB
Jim and clan, Any gain for MGB's/British cars to run headers,"forward" of engine, and then sweep back? How about through rocker panels ? 2 cents,roverman.
Jim, what I've got out of Dan's advance explanation (and what I've also read so far) is that there's a small window of opportunity to scavenge exhaust and help draft in a new oxygen rich charge; that small opportunity reveals itself at a hard to define exhaust location/length. Most of the factors that he talks about affecting this area are before the mufflers; any source after that becomes a possible restriction to that important scavenging/filling process.
In what I've also gathered, proper muffler inlets can help setting the tone for what ever good is supposed to take place in that muffler (sound control and flow, etc.) and how dropping the seize of the tailpipes can ruin the prior well tuned process by foresee ably applying back pressure. I just don't see any reasons to reduce the tail pipe seize other than making it easier to bend and fabricate smooth turns, however, I do see a single concern, "back pressure" but having said that I like yourself wonders where the justification/danger occurs? I'm also still puzzled on the "H" or "X" pipe principles?
Auto manufacturers are faster in drawing a line to avoid manufacturing complications and cost savings than a performance purist is willing to. After all these years, they've come to realize that some SEMA member will take on costly performance challenges for profit.
I'm not sure if other than getting a strong lesson in "performance exhaust" I have a better plan to operate by. I'm also still undecided if I should use an "H" pipe, mufflers and resonators, or just mufflers. I may also find it too difficult making 2-1/2" tail pipe bends, so what is the lost? One thing that I can be sure of is the fact that I don't want anything to lesser the money invested in the full potential of my engine.
BTW, Dan I'm considering moving up to the 70 MM throttle body as you suggested since I've already have a set of 30 pounds injectors. You've mentioned a possible 385 H.P. on the engine dyno, what would translate to at the rear wheels? There's also a worthy modification to do on the GT-40 intake that is well justified by the flow increase.
I hope that I don't wear my welcome out on this thread but I really enjoy reading everyone's comments or helping anyone out if I possibly could.
Jacques
In a perfect world there'd be no bends. (BTW, if anyone's wearing out their welcome it'd be me so don't worry, be happy.)
Dirt bike riders found that removing the spark arrester from the scavenger pipe made the bike louder but actually caused a slight decrease in power. So if a smaller tailpipe is always going to increase restriction, why is that? Shouldn't power go up? I'd say it's because it changed the resonance of the system.
I don't buy for a minute the idea that beyond the muffler the tuning of the system as a whole has no effect. I'm sorry for being hard headed about it, but the entire system from end to end does have a resonance, and that resonance can effect the engine I believe. If you are tuning for maximum power, then yes, perhaps going as large as is practical there makes sense, but if you are tuning for some measure of fuel economy, and therefore looking for resonance at a lower engine speed I think it likely that a smaller tailpipe makes sense. Does a longer exhaust system add nothing but back pressure? Or did the testers overlook other potential advantages because they weren't looking for those results?
Please understand, I'm not disagreeing with Dan's theories, but he is oriented towards maximum performance and as far as I know always has been. I've gone down that road but with any engine, going for maximum output not only has no limit, it's cost runs to infinity. So my approach is to use less expensive methods and seek to achieve maximum performance at minimum cost, both in development and in operation. There is much to be learned from Dan's approach that can also be used in mine, and perhaps occasionally vice-versa. So where Dan promotes a particular approach for power, and that will probably be appropriate for many applications including many forms of sanctioned racing, I am inclined to take more of an outlaw approach, and one which not only does not conform to racing rules in any forum, but tends to go outside generally accepted norms in other ways too. Because of that I will frequently challenge the generally accepted principles, and I will often be right. It doesn't mean you should follow me, but it may give you more to consider.
Now, I don't have the resources to do some of the testing Dan does, and I'm a great believer in test results. So where the test conditions are known and the results verified, I strongly believe in making use of the results. But before I will buy into a flat statement, especially about something as complex as an exhaust system, I'll have to see results from back-to-back testing of competing theories using setups that accurately portray those theories and do it under the appropriate test conditions. For instance, you may get more power across the board with a larger tailpipe in a given car, engine and exhaust system combination, but was the test also run to determine relative fuel consumption at different road speeds? Even if it was, if you change the vehicle, the engine, the headers, or even the muffler the results could be dramatically different. So I don't just automatically accept that what works for one car transfers straight across to another. The problem of course is that formal testing can be prohibitively expensive, whereas informal empirical testing is usually very time consuming, difficult, and also not cheap.
JB
Jim, as a youngster (17) I had a snowmobile with a two cycle Rotax motor. It ran great for a long time until I removed the muffler and replaced it with a megaphone; three engines later and many carb re-jetting, I went back to a muffler but a tuned exhaust type (funny looking). As far as I know, two cycle exhaust behaves totally different than a four cycle exhaust, "brother from an other mother eh!"
Yes I have heard that said, but why would it? So far nobody has presented any fundamental reasons why that would be the case. You have the expansion of the exhaust pulse in a scavenger type pipe of course, presumably to the point of collapse of the pressure front but that is by design of the exhaust header, not the engine. Is there any reason why the same principle would not apply to a 4 cycle design? I'm just asking. Obviously the biggest difference is that the 2-stroke has a lot more overlap, and without either a very good extraction or very good transfer function it just won't run, or won't run well. Fundamentally, why would good extraction be any less beneficient for a 4 stroke engine? Again though, this is theoretical because the practical considerations make an expansion extractor system for a V8 a non-starter, as it would take as much room as the engine itself, or more. But the example was to illustrate the point that the outlet is as small or in many cases smaller than the inlet. Are we to assume that because of the dynamics of the expansion chamber the outcome is somehow different? The "black box" representing the exhaust system between the port and the tailpipe somehow makes one tailpipe a restriction but makes the other just the opposite? It needs a better analysis to make that argument palatable.
So I'll go back to what I said before. You have to pick a point in the spectrum for your own application. In a perfect world with no compromises there are no bends and the exhaust operates at maximum efficiency, whatever that is, whether via megaphone or whatever is the best, most optimized approach. In the real world though we live with all kinds of auxiliary considerations and have to balance out the concerns of one against the other. Size of the tailpipe is one such, especially if routing it over the axle. Ground clearance is another. Obviously your mileage will vary greatly depending on where you put your priorities and you may well find that with a given vehicle and engine that a 2 or 2-1/4" set of tailpipes do not hurt performance enough in your operating range of the engine to make it that much of a concern. Would I give up 20 hp to route the exhaust high in an MGB with a 400 hp engine? I probably would for a purely street driven car, because I've already come to the conclusion that at 300 hp the car is more than capable of blowing the doors off at least 99% of the cars out on the street and to do so very convincingly. (That's a 8:1 weight to HP ratio BTW, 380 is about 6.3:1 and 400 is 6:1) The benefits outweigh the disadvantages. Besides, how often am I even going to see that one guy who I can't outrun, and even then how often am I going to feel like racing him? I don't live in a small town anymore and bragging rights just aren't that important. Aside from that, I subscribe to the Carl Floyd school of competitive driving, even if I do like horsepower, and the skill of the driver can often more than make up for a difference in the engine.
JB
Jim and clan, don't the rules change for forced induction ? Do you not enhance boost by cutting back on valve overlap and exhaust duration ? 1 3/8" for 600 hp. jus' don't sound rite, lol. roverman.
Funny Art ;-)
I never claimed 600 HP. Last I checked I think I was saying I expected to make something upwards of 300. I think 1-3/8" should support that just fine. (and my lobe centers are at 112*, not sure what the overlap is, it was supposed to be ground explicitly for a blower engine)
This is not your typical max performance engine, and is designed with specific goals in mind, including a wide powerband and extended rpm range (up to 7000). It is not expected to continue significantly building power above about 5500, but to be capable of the higher speeds to add flexibility in gear selection, i.e. not having to shift in the middle of a curve.
MVC-707F.JPG
JB
> I'm also still puzzled on the "H" or "X" pipe principles?
Cross-overs work by one of two different principles. On an engine without
mufflers, if you could watch the flow in the cross-over, you'd see the exhaust
move only a few inches back-and-forth. In an open exhaust, the cross-over works
by acoustic tuning, transferring shock waves. On an engine with mufflers, they
allow the cylinders on one side of the engine to share the muffler flow of
the other side. While they don't double the muffler flow, a 25% increase in
apparent muffler flow is possible. Vizard has test both H-pipe and double
cross-over systems. The double cross-over looks like an X-pipe superimposed
upon a dual exhaust but is not a simple X-pipe. Vizard's testing indicates
the H-pipe version only works with mufflers that already flow very well in
relation to the engine's power (i.e. have low operating back pressure). Placement
should be as near to the header collectors as possible. On less efficient mufflers,
the double cross-over works better.
> You've mentioned a possible 385 H.P. on the engine dyno, what would translate
> to at the rear wheels?
A little over 300 RWHP (305 to 310 RWHP).
> Is there any reason why the same principle would not apply to a 4 cycle design?
> Obviously the biggest difference is that the 2-stroke has a lot more overlap
The fundamentals of tuning (inertial scavenging and finite amplitude waves) may be
the same but the required plumbing and the resultant effects are different between
2 and 4 strokes and between 4 strokes of different piston layouts (single cylinder
versus inline 4 versus 90 degree V8).
> going as large as is practical there makes sense
There are optimal lengths and diameters for a particular engine in a particular
operating range, exceeding them with larger sizes will reduce performance,
as will smaller. That said, some parts of the system are sensitive to sizes,
others are not (more on that below).
> he is oriented towards maximum performance
Performance can mean many things. It may mean maximum HP but it may also mean
maximum fuel economy. I try to maximize the system within whatever set of
parameters I'm handed. For instance, I'm currently working on one SBF that is
constrained by the diameter of the exhaust pipe that runs through the convertible
bracing and by a goal of 20+ MPG on the highway.
> So I don't just automatically accept that what works for one car transfers straight
> across to another.
Nor do I. That's why I've been testing Dynomation against a variety of dyno tests
on engines ranging from a 200 HP Rover V8 with tiny inline valves to a 650 HP 407
cubic inch Cleveland Ford with canted valve high port heads. The basic physics is
the same but those two engines behave very differently because one is limited by
the port area and the other is not. The fundamental differences between a 2 stroke
single cylinder engine and a 4 stroke V8 are much larger so why would you think
tuning for the 2 stroke directly applies to a 4 stroke? My 2 stroke experience is
limited but I've never seen any 4 stroke exhaust tuning respond like a 400 Kawasaki
2 stroke as it comes on the pipe.
Back to the problem at hand. Small and large re relative terms and some parts of
an optimal exhaust system are less sensitive to change than others. A straight
pipe of certain cross-sectional area flows quite well compared to a muffler with
the same ID. If you can't fit 2 1/2" diameter intermediate pipes, 2 1/4" pipes may
work well as long as you step up the muffler ID to 2 1/2". With the SBF we've been
discussing, reducing the collector outlet diameter to as little as 2.5" may slightly
hurt peak power potential but will likely have only a small penalty (or perhaps none
at all) on average power between the shift points. In the Engine Masters Competition,
the guy I run the Cleveland Ford dyno program with (Dave McLain) and Kaase both found
the best results with a 3" diameter collector on engines that made upwards of 660 HP.
That competition was scored on a best average power between 2500 and 6500 RPM. While
they could make better peak power with larger ID collectors, they gave up more power
lower in the RPM range so the averages suffered. Avoid reducing diameters at curves
like those at the axle hop as a curved pipe flows less than a straight pipe and use
smoothly bent pipe. I've not personally tested using a smaller tail pipe size to
see the direct effect but you can test it with a pressure gauge.
> I am inclined to take more of an outlaw approach, and one which not only does not
> conform to racing rules in any forum, but tends to go outside generally accepted
> norms in other ways too
Jim, have you read The High Speed Internal Combustion Engine by Sir Harry R. Ricardo?
Funded to develop piston engines for the war effort, Ricardo did so without any
regard to class rules. His work is at the base of everything hot rodders do, whether
they realize it or not.
Dan Jones
I'm seriously considering "merge collectors", for the 290" Huff GT 1 motor. I suspect there are gains over conventional 4 into 1, but I would like to see some science. Thanks, roverman.
I found this interesting:
http://www.southernskies.net/page_info/runningtwostrokeengine.html
Carl, that's a pretty darn nice site you've found; perhaps if something similar could be found for the four stroke engine it would help us better understand the difference between the two.
It also reminds me how EFI intake runners are tuned to length in order to create a resonance/pulse bounce that helps push in the air charge into the cylinders. IMHO, this thread has been highly educational for lots of us; between Dan and Jim I'm starting to feel a little more confident in my exhaust design.
Jacques
Thanks Dan, I have made a note and will check at the local library next time I go there, perhaps they can get it. Sounds like an intriguing read.
Carl, that is a real find on the scavenger pipe. The author obviously knows his stuff. What I picked up on was the function of the reverse cone in ramming the escaped intake charge back into the cylinder, that was really the piece of the puzzle that I was missing, and very effectively and simply explains why the pipe is both extremely effective and very sharp in cut-off (peaky).
This makes it child's play to explain why the scavenger pipe would not be effective on a 4 stroke engine.
"This pulse is timed to reach the exhaust port after the transfer ports close, but before the exhaust port closes. The returning compression wave pushes the mixture drawn into the header by the negative pressure wave back into the cylinder, thus supercharging (a bigger charge than normal) the engine. The straight section of pipe between the two cones exists to ensure that the positive waves reaches the exhaust port at the correct time"
In this version of the 2-stroke the transfer ports take the place of the intake port. Obviously in a 4 stroke the intake does not close before the exhaust valve so this effect could only be used with a custom ground cam with an extra bump on the exhaust lobe. I don't know if anyone has ever tried that but it would be pretty impractical for a V8 due to the size of all the individual scavenger chambers, especially given the larger displacement of each cylinder. It might be made to work with something like a Briggs & Stratton racing class possibly. However, it still does not explain what is going on with the small diameter "stinger", (closed ended pipe, I got that part) and how that compares to the typical V8 system. It is clear enough that a pressure pulse after each firing ejects a quantity of exhaust from the stinger, and this is clear to see when the bike sits and idles and the oil begins to build up smoke in the exhaust. But I think there is more to this story, some of which we might make good use of. In particular, I don't think we've given enough attention to the temperature decreases from end to end, nor to the smoothing of high and low pressure pulses later in the system. If you look at pressure curves for gasses it's pretty clear that the needed volume for a given pressure increases substantially with temperature. In a typical exhaust system we're dropping *hundreds* of degrees in temperature from one end to the other, in most cases well over five hundred degrees. I think we need to have a look at exactly what that means to us in terms of system pressure, and therefore flow requirements.
JB
Why not the best of both worlds, The" on demand 2/4 cycle engine". This was/is, designed/tested by Ricardo Research Foundation. International Patents. Impressive performance and economy. roverman.
Jim, I observed the same thing off of Carl's link; this type of tuned scavenger muffler made a huge difference on our snowmobiles, however, it had to be built to the exact (specific) engine application.
I believe that this is what Dan was explaining all along, a well designed four cycle exhaust at its best can create the necessary low pressure trail (vacuum like) that finishes the cylinders charge filling. There's a muffler that I'm interested in that has its inlet designed to compliment the scavenging effect; surprisingly, it's only sold with the same seize outlet.
Jim If I understood you right, one comment that you've made is that whatever horsepower gain or lost resulted from the exhaust was no big compromised on a 400 H.P. engine, I agree, but, the only worthwhile result should be at the rear wheels, hence, the well built exhaust dictates that rear wheel result. I'm sure that it also helps the engine rev a lot quicker/straight up (torque?).
It's hell to know just enough to get yourself in design trouble but not enough to work yourself out of it without the help of knowledgeable comrades like you and Dan, and brother, I thank you for that help.
Cheers,
Jacques
This thread doesn't have enough photos, so I thought I'd stir the pot by posting photos of something I don't think has been talked about yet: anti-reversion devices for four-stroke headers. (Photos from an upcoming article...)
(http://www.britishracecar.com/JeffSnook-Alexis-Mk14/JeffSnook-Alexis-Mk14-BH.jpg)
(http://www.britishracecar.com/JeffSnook-Alexis-Mk14/JeffSnook-Alexis-Mk14-BG.jpg)
ref: http://www.hytechexhaust.com/who_we_are/who_we_are.htm
(http://www.hytechexhaust.com/images/whowe/reversion01.jpg)
QuoteREVERSION is the secondary pressure wave that travels back up the primary pipes and enters into the cylinder on valve overlap. As this pressure wave travels back up the pipe, it brings with it all the residual gases still left in the pipe. This is what contaminates the fresh intake charge. Enter in stepped headers and ANTI-REVERSION chambers, placed at strategic locations in the primary pipes. These methods are employed to tune the arrival of the exhaust wave and to diminish the effects of the high pressure in the pipes. The results are higher volumetric efficiency and more power.
Thanks Curtis. I notice it uses a "merge collector". Can we now have some science, to go with these power inducing thingies ?roverman.
Unfortunately, I don't know much about the thought or testing behind HyTech's headers. I'm keen to hear any comments or insight here! (I've photographed two Formula Fords that use them. Interestingly, the two car owners both told me the headers came about a foot longer than shown above. They trimmed the tail end for practical/safety reasons.) Am I correct to think the primaries are paired oddly compared to regular tri-y headers?
Curtis, I think tri-y headers are refering to V8 applications ? "Bank" firing order, is usually different from L4's,(except for "Freds"miraculous, flat plane, 180 firing, 32 valve, RV 8) ! Go gettum Fred ! roverman.
Vizard covers anti-reversionary headers in "Performance with Economy".
His testing was on a V8 with bank separated 4-into-1 headers with the AR
cones built into the flange. The cones act as a diode, allowing flow
out of the exhaust port but not back in and are less sensitive to larger
primary sizes (though you should still pick the best diameter for your
operating range). His conclusion was that AR headers work well, providing
better fuel economy and power but a cross-over is mandatory. Also, the
carb will need to be retuned as the AR headers provide a stronger signal.
The extra power comes primarily in the low and mid-range if the primary
pipe diameter is held constant. One example cited was a 305 SBC powered
Malibu that went from 17 to 21 MPG with no other changes other than fitting
AR headers. Another example was an engine that wouldn't run smoothly below
4000 RPM due to reversion was able to run at 3000 RPM. Blackjack and Cyclone
were the holders of the patents but have since been bought out and, AKAIK,
the AR line was dropped. You may be able to buy pre-made flanges from a
company like Headers by Ed. The Japanese import crowd have been using AR
chambers in the primaries similar to the exhaust shown.
Dan Jones
Here's a link that explains exhaust almost to perfection:
http://www.popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/index.html
Not much said there about the resonator cones. It occurred to me that I'm in a perfect position to add those to my system as I have to shorten the pipes about an inch due to added engine width. Somehow I keep removing simplicity. Now the question is the best method.
One point I'd like to add is that the recommendation in using the primary sizing chart was to concentrate on the "RPM range of interest" in determining primary size. Note that the closest thing to rpm given was the amount of flow, so if your primary range of interest is daily driving the flow rating will be a mere fraction of what it would be for maximum performance, and better to err in a downward direction. So then, if your heads flow 150-200 cfm but you only put your foot in it on rare occasions, maybe those 1-5/8" primaries aren't needed.
Another point, relating equal length primaries to race engines where a <3000 rpm band makes such unnecessary, in street driving, and especially spirited mountainous driving where the desired usable RPM range can be in excess of 4000 rpm easily, equal length primaries make a whole lot more sense.
YMMV
JB
Jim, are you expecting to have "reversionary flow" problems, with that bad-boy blower strapped on there ? Going to dyno this build ? Measure "pressure" in the exhaust ? If so, I suspect you'll find 1 3/8" primaries, overly restrictive ? Good Luck, roverman.
Doubt they'll be any more restrictive than the exhaust valves and ports. Remember Art, this is not a max HP project. Despite the blower, the goal is not ultimate top end performance, but all around driveability and good economy. Adequate power will be there. There is nothing to choke power down to levels below what I was producing with the 215, which was in the 300hp range and the headers were quite adequate for that application. If you'll recall, Vizard's recommendation was to err downwards in tube size, and I also had the opportunity when they were built to pick the brains of Ed Henneman ("Headers by ED"), one of the most knowledgeable exhaust system guru's on the planet at the time. (mid 80's) The tube size was optimized for a 300 cu.in. engine so yes, for a normally aspirated 350 at full tilt-n-boogie it'd probably be a little undersized and a few ponies might be lost at the top. But for a blower motor that is going to spend 99% of it's life under 4 grand? Even if it does see 7 on occasion I think these tubes are going to turn out just fine. Remember, I consider 300hp in an MG to be adequate and the goals of durability and low maintenance are equally important. I could put a cast iron manifold single exhaust on the car and meet that goal sitting in the shade, so how are those 1-3/8" primaries going to hurt?
JB
On the dyno question,.... maybe. I'm not sure what real purpose it'd serve. I'm not aware of a shop that has one around here so it's an investment in time and money that can be better spent other places.
> One point I'd like to add is that the recommendation in using the primary
> sizing chart was to concentrate on the "RPM range of interest" in determining
> primary size. Note that the closest thing to rpm given was the amount of flow,
The amount of flow is a function of the valve lift for a given cylinder
head, not an indicator of RPM. If you click on the graph, the primary
sizing curves are explained:
"Fig 4 This chart applies to normally aspirated engines. For street headers,
where low-speed torque is of prime importance (especially with a stock
converter and high rear end gears), use the lower line to select the
appropriate primary size. For hot street machines having reasonably big cams
and decent compression, use the middle line to size the primary. For race
engines, use the top line. If nitrous is involved, check out the nitrous header
section."
The lower curve is best applied to heavier vehicles with automatic
transmissions and/or tall final drive ratios and would be conservative on a
lightweight British car with a big American V8, a 5 speed, good cylinder
heads and a decent cam. AFR 165's flow nearly 190 CFM on the exhaust side
(184 CFM @ 0.500", 188 CFM @ 0.0600", 189 CFM @ 0.700"). Assuming a cam
with modest 0.5" lift on the exhaust side, even the lower curve calls for
1 5/8". Furthermore, a 5.0L HO with the stock E7TE heads only flows around
110 CFM at the same lift (grinding out the Thermactor bumps will help that
some) and Ford's stock tubular exhaust manifolds were sized at 1 1/2".
I'm working on a SBF with Floo Tek heads where I may use 1 1/2" primaries
for clearance reasons. The Floo Tek heads are cast in Australia, assembled
in Indy and are essentially copies of the FRPP GT40 turbo swirl heads. They
flow around 160 CFM @ 0.500" lift on the exhaust side. They will be used in
a 1971 Mustang convertible with 2.79:1 final drive ratio and an automatic
overdrive transmission with 2500 RPM stall speed. With an HO servo, the
transmission up shifts around 5200 RPM and there is only room for 2 1/4"
intermediate pipes through the convertible chassis bracing (though I'll
likely step up to 2 1/2" for the axle hop and Magnaflow mufflers). If the
same engine were in a lightweight sports car with 5 speed manual transmission,
I'd for sure use 1 5/8", especially with heads like the AFR 165 with their
excellent exhaust port. That assumes there is space permitting. On the
convertible Mustang, I'll be running simulations to compare primary diameters
and collectors to help me make up my mind but I think the 1 1/2" primaries
will be okay if I optimize the collectors.
> where the desired usable RPM range can be in excess of 4000 rpm easily,
> equal length primaries make a whole lot more sense.
The paragraph following that discussion explains that, even with equal lengths,
much of the potential benefit is lost in V8's that use a dual plane crankshaft.
Things would likely be different with a flat plane crankshaft. Also be aware
the presence of bends changes the apparent primary length. 180 degree headers
are much more sensitive to equal lengths and one builder of such headers I know
sizes the lengths acoustically so that each pipe tunes in on the same note.
You'll usually find better payoff by concentrating on the collectors. It's
relatively easy to change collector length and styles. One of the SBF drag
racers I know has had very good results with the merge style collectors on
evrything from a relatively stock fuel injected 5.0L to a high winding 289.
Dan Jones
It's also interesting to note what some of the SBB guys are doing with ported stock exhaust manifolds. Getting into the 12's with full sized cars running the 350 small block and cast iron manifolds, they claim about a 5-10 hp loss over tubular headers. That's 2nd hand, but those boys are fairly serious about their drag racing so even if it's padded a little it's still sort of impressive. The Buick manifolds are a pretty free flowing design.
JB
> It's also interesting to note what some of the SBB guys are doing with
> ported stock exhaust manifolds. Getting into the 12's with full sized
> cars running the 350 small block and cast iron manifolds, they claim
> about a 5-10 hp loss over tubular headers. That's 2nd hand, but those
> boys are fairly serious about their drag racing so even if it's padded
> a little it's still sort of impressive.
The biggest difference between exhaust manifolds and long tube headers
tends to come at lower RPM (see my dyno data at the bottom). Also, the
can be 20+ HP difference among different long tube designs. I'd wager
those Buick headers aren't optimized and/or there is a much larger
difference at lower RPM. The best of the SBF iron manioflds were the
K-code 289 hipo manifolds. A better alternative would be the 5.0L HO
Mustang tubular steel "shorty" manifolds. In addition to the OEM, there
are a wide variety of aftermarket versions available in 1 1/2", 1 5/8",
1 3/4" and 1 1/2" to 1 5/8" primary diameters, equal and unequal lengths
in mild or stainless steel. Long tube headers still out-perform them but
they are useful where stock location catalytic converters must be retained
for emissions purposes or where long tubes won't fit.
Here's a magaxzine test of stock, K-code and long tube headers on a
dynojet. Note it's a fairly mild 302 engine, through the mufflers and
the power is at the rear wheels.
http://www.mustangandfords.com/techarticles/mufp_0607_ford_mustang_performance_exhaust/index.html
There's another test which recorded a much bigger differnce on a 347 SBF
stroker:
http://www.mustangandfords.com/techarticles/engine/5157_headers/index.html
They claim 104.5 hp and 96.6 lb-ft of torque difference between Hooker
Super Comp headers and K-code manifolds. though it appears they also
installed a K&N air filter at the same time.
> The Buick manifolds are a pretty free flowing design.
The Ford 351C-4V engine has larger valves (OEM size is 2.19" diameter
intake and 1.71" exhaust) and their iron exhaust manifolds have
ports that are much larger ports than a Buick 350. Here are
the results from dyno testing I conducted on a fairly mild
Ford 351C. At 4200 RPM, where we started the pull, the iron
manifolds are down 59.1 HP and 72.6 ft-lbs of torque. It
would be even worse down at 2500 RPM. This is because of the
short length of exhaust manifolds. The long tubes are able to
tune in at a lower RPM. The gap narrows at higher RPM but is
still 26.5 HP at 6100 RPM. Note that the long tube headers
are no where nearly optimized for this combination. Still,
if you plot this data, you'll see the difference in area under
the curve is huge (more than you'd likely get from an expensive
set of aftermarket heads or port job). Couple this with the
50 HP difference in mufflers we saw and you can turn a 400 HP
engine into a 300 HP with a restrictive exhaust.
Ford 351C-4V Dyno Project Engine
hydraulic roller street cam
flat top pistons
unported iron 351C-4V heads
12 inch extension and Magnaflow mufflers
Iron 351C-4V Exhaust Manifolds Hooker 1 3/4" primary headers
RPM HP Torque (ft-lb) RPM HP Torque (ft-lb)
4200 259.7 324.9 4200 318.8 397.5
4300 274.3 334.7 4300 325.0 397.7
4400 284.8 340.1 4400 331.6 395.9
4500 294.8 344.0 4500 339.4 396.1
4600 305.4 348.7 4600 349.9 399.2
4700 315.1 352.2 4700 360.6 402.9
4800 330.1 360.6 4800 368.0 402.8
4900 343.2 368.8 4900 372.4 399.5
5000 345.5 363.1 5000 378.0 397.0
5100 354.0 364.2 5100 388.6 399.7
5200 364.8 368.7 5200 397.1 401.1
5300 368.6 365.4 5300 401.3 398.2
5400 377.5 367.0 5400 404.9 393.8
5500 382.5 365.5 5500 409.9 390.9
5600 383.0 359.2 5600 412.1 386.7
5700 384.7 354.4 5700 407.9 375.8
5800 383.8 347.0 5800 401.4 363.8
5900 376.6 335.6 5900 398.9 355.1
6000 369.3 323.2 6000 401.3 351.2
6100 380.5 328.4 6100 407.0 350.2
Dan Jones
For the record, are we discussing ID. or OD. on tubing sizes ? Any solid data on merge collectors ? Stepped primary headers, properly built, function similar to anti reversion cones? Port mismatch at port can be "a" on flooor, "b" on sides, and "c"never on roof ?. Why not use oval tubes to fit available spaces ? Is it not the "area" inside the tube and bend radii ?Thanks, roverman.
Good info Dan, about the hp/rpm losses and the area under the curve. I have long been a believer in chasing that volume vs. absolute hp peak so to me this is very revealing (and to be honest, 5-10 hp loss sounded like pie-in-the-sky). I'm also a firm believer in long tube headers for the street. Art, I can't speak to others' comments but my measurements were inside diameter.
About the anti-reversion cones, I looked at some test results (Harley) and the graphs I saw showed no gain and an upper end loss due to restriction. These were slip-in cones that are simply inserted into the end of the header pipe. Starting to sound like snake oil, and I'm suspecting that any advantage is going to be in a very specific application under ideal conditions (racing perhaps). Without more than that they would hardly be worth the trouble. But having said that, a Harley exhaust is hardly an ideal tuned system. Also it seems they were primarily interested in eliminating a dead spot in the power curve where reversion was thought to be interfering and causing a power loss. All of this leads me to suspect that a properly designed set of headers is not going to have much of an issue with reversion and therefore the cones will be of little benefit.
JB
> For the record, are we discussing ID. or OD. on tubing sizes?
The data is for ID. Headers vary in their wall thickness with street headers
typically having thicker walls compared to race headers.
> Any solid data on merge collectors?
I've not personally tested them yet but will likely in the future on
mid-length Pantera 351C headers. However, a SBF racer I know has installed
them on both his car and his son's (both record holders) and gone faster.
> Stepped primary headers, properly built, function similar to anti reversion
> cones?
Stepped headers approximate a constant taper angle. I'm not sure if the
abrupt area changes have an effect on reversion or not. If so, the mechanism
would be different (via finite amplitude waves).
> Good info Dan, about the hp/rpm losses and the area under the curve. I have
> long been a believer in chasing that volume vs. absolute hp peak so to me
> this is very revealing (and to be honest, 5-10 hp loss sounded like
> pie-in-the-sky).
Agreed. Peak numbers are irrelevant. The area under the curve in your
desired operating range (between shift points) is what really matters.
> About the anti-reversion cones, I looked at some test results (Harley) and
> the graphs I saw showed no gain and an upper end loss due to restriction.
> These were slip-in cones that are simply inserted into the end of the header
> pipe. Starting to sound like snake oil, and I'm suspecting that any advantage
> is going to be in a very specific application under ideal conditions (racing
> perhaps).
On a two plane crank V8 with bank separated 4-into-1 headers, Vizard's
testing indicated the AR effect required a cross-over to work. That
testing used cones in the header flange.
> All of this leads me to suspect that a properly designed set of headers is
> not going to have much of an issue with reversion and therefore the cones
> will be of little benefit.
Reversion is more of an effect of the cam overlap, particularly the component
provided by narrow lobe separation angles. Reversion occurs at lower RPM,
so don't expect to see any benefit at higher RPM. Vizard's testing showed
the largest effect occurred at low RPM and trailed off as RPM increased.
He presents before and after testing in both "Performance with Economy" and
"How to Build Horsepower, Volume 1". BTW, Vizard has a new version of "How
to Build Horsepower" coming out. The second edition appears to replace
Volume 1 (an overview that covers everything). Volume 2 covers induction
(carbs and intake manifolds).
Dan Jones
>Jim, have you read The High Speed Internal Combustion Engine by Sir Harry R. Ricardo?
>Funded to develop piston engines for the war effort, Ricardo did so without any
>regard to class rules. His work is at the base of everything hot rodders do, whether
>they realize it or not.
>Dan Jones
I'm not sure if you realize it Dan, but this book costs ~$350.00, not the sort of thing the average guy just goes out and buys. My local library is trying for an intra-library loan but I'm not holding my breath.
But I did run across a Vizard book in my personal library and will look it over again during thanksgiving.
Happy Turkey Day all. Let's not forget how we got here.
JB
"Happy Turkey Day all. Let's not forget how we got here. "
The Pilgrims could have got here faster if they had stuck a V8 in the Mayflower!
>I 'm not sure if you realize it Dan, but this book costs ~$350.00, not the sort of thing the average
>guy just goes out and buys. My local library is trying for an intra-library loan but I'm not holding my breath.
Oh come on. There's a bunch of used ones on Amazon for as little as $250. !! :)
Martin
Reportedly, the Pilgrims had a"Ford" in their fleet,(Pinto). Is that why it tookem soo long ? Perhaps "Sir Harry" charges soo much, posthostumously, is because his brother,"Ricky", got all the Press ? lol. and Happy Pilgrim Day.roverman.
Dan,
Did I read somewhere above that your expecting 350 BHP from your 4.2, I built a stroked 3.9 with 4.2 crank, 5.85" Chevy rods and flat top with cut outs 305 Hypereutectic KB pistons to give 4350cc.
I have modded alloy 300 heads with 1.63" In and 1.4" Ex. with the seats taken out to actual seat size and the throats and bowls all blended to match, port runners are left as standard with a minor clean up as specifically for road use.
Static comp ratio a bit lower than I would have liked at approx 9.4/1
Induction system is currently Edelbrock 500 and manifold and exhaust is a RV8 through the inner wings system with single pipe.
Cam is Crower 50232
Ignition is a recurved lucas 35DLM8
Haven't had it dynoed as the result from rolling roads seem to vary wildly, what would you think it should produce, I was aiming for 260+ BHP.
Regards,
Kevin Jackson.
Hey Jim,
Ricardo's book is available to read on line.
It's been a while and I was never able to print it but I'll try and find the address again for you.
Cheers
Fred
Thanks Fred, I'd like to see that. It turns out my library was able to get it for me and I've had a few days now to read it. A wealth of information there. I particularly liked this passage:
"...the finest achievement ever reached in any sphere of mechanical engineering, for it constitutes the best example of what can be accomplished by the co-operation of the scientist and the practical engineer working together in harmony. In every successful example it will be found that the actual designer of such an engine is neither a great scientist nor an expert mechanic, but an artist with an artist's temperament and intuitive genius, though none the less ready to appreciate and accept all the aid that the scientist and the practical mechanic can give him, and competent to blend his and their conflicting demands into a perfect picture. Such men are rare and in any one country can be counted on the fingers of one hand. Without doubt the greatest of them was Sir Henry Royce."
Sir Harry R. Ricardo: The High Speed Internal Combustion Engine pp. 280-282 (5th edition reprinted 1972)
To that I'd like to add a quote of my own:
"Aim high. You may fail miserably, but you will also know moments of true greatness. For this there is no substitute."
JB
> Did I read somewhere above that your expecting 350 BHP from your 4.2
Using the flow numbers from my GM race heads, Dynomation predicts between
323 and 359 HP, depending upon how efficient the single plane intake is.
The GM race heads were designed for Mickey Thompson's Indy car effort and
Lance Reventlow's mid engine Scarab. Compared to my ported Buick 300 heads,
they GM race heads are better on the exhaust but worse on the intake due
to the smaller intake valve size. On the flow bench, the exhaust flows
173 CFM at peak compared to an unported Rover flow of 92 CFM. Because of
the strong exhaust port, a custom cam was required to match the flow
characteristics to maximize the horsepower.
> I built a stroked 3.9 with 4.2 crank, 5.85" Chevy rods and flat top with
> cut outs 305 Hypereutectic KB pistons to give 4350cc. I have modded alloy
> 300 heads with 1.63" In and 1.4" Ex. with the seats taken out to actual
> seat size and the throats and bowls all blended to match, port runners
> are left as standard with a minor clean up as specifically for road use.
> Static comp ratio a bit lower than I would have liked at approx 9.4/1
> Induction system is currently Edelbrock 500 and manifold and exhaust is
> a RV8 through the inner wings system with single pipe.
> Cam is Crower 50232
> Ignition is a recurved lucas 35DLM8
Entered into Dynomation.
> Haven't had it dynoed as the result from rolling roads seem to vary wildly,
> what would you think it should produce, I was aiming for 260+ BHP.
With my ported Buick 300 heads with Stage 1 Buick V6 valves, the prediction
is 279 HP. With unported Buick 300 heads and standard valves, the prediction
is 232 HP. Unported Buick 300 flow numbers but your valve size, the prediction
is 238 HP. Adjusting the throat sizes gets 242 HP. Your flow numbers would
be somewhere between these two, figure something between 240 and 280 HP,
so your 260 HP guess is in the ballpark. These use the dimensions of the
Performer Rover dual plane intake and an assumption that is "standard flow".
If the intake assumption is "high flow", expect 15 additional HP. If you have
space for a plenum spacer, that would help the intake rating and increase the
peak power. I'd need your actual cylinder flow numbers and min/max port sizes
to be more accurate.
Dan Jones
Hey Jim,
So here you go.
www.scribd.com/doc/40610101/The-High-Speed-Internal-Combustion-Engine-by-Sir-Harry-Ricardo
It just boggles my mind that one man could have such a firm understanding of all these principles so long ago.
90 years on, with countless hours spent by countless people, and no one person understands these principles any more completely than he did.
Cheers
Fred
Thanks Fred. He was impressive no doubt. Since that is the 2nd edition it will be interesting to see what he changed between that and the 5th edition. Some 40 odd years was bound to have made a difference.
JB
Thanks Dan.
Yes forgot you were using those specially cast heads.
Kevin
Ok, Most will accept that 4 into 1 merge collectors, add power. What about a "gullet" in center of the 4 pipes,inside the collector ? Old skool therom of up to 10 hp gain for conventional 4 into 1 collectors,(2). roverman.
To Dan Jones:
I sent you a PM in regard to this thread last night... Hope you are still watching and can reply.
In the meantime, thank you again for all your valuable guidance!
Cheers,
Mark Griffin