Opinions on this "recipe" please

[cfarmer]

Okay, I'm taking the plunge - my first real post.  I've been lurking for a while, and have come to realize that there's a lot of free expertise out there, so I'm looking to capitalize on it.  I'm collecting parts for the following motor (for my TR4) for street/strip use  - and am hoping for some insight from the knowledgeable folks on the forum to keep from making any "big" mistakes.  

I've got a 1990 3.9L long block that had a spun rod bearing, but is otherwise in great condition.  I plan to bore it to 3.736.  I recently purchased the 77mm crank from a 4.2L motor, and plan to use these with 6.0" chevy small journal rods (narrowed big ends) and 10cc Keith Black 186 or 834 pistons (chevy 305) with 1.433" compression height.  From the posts I've read, I believe there are a couple of you that have, or are building, very similar motors.  I plan to use the 3.9L heads but I've also got buick 215 heads (and the short block) as well.  Head gasket would be from the Buick 300 which I believe has a 3.750" bore and 0.040" compressed thickness.

My calculations show this combo would give me 10.85:1 CR and 0.052" quench.  Intake is the Edelbrock Performer (until I can afford one of the single planes).  I've got a 600 CFM Holley that I hope to use as well.  The cam would either be the Isky 270 or 282.  

I'd really like some advice on bigger valves for the Rover 3.9 heads.  Are the 1.63/1.40 valves from various UK sources the way to go, or can I make the 1.625/1.425 valves from the Buick 231 V6 (early) work.  How much do I have to worry about the length?  I've probably written too much for a first post, maybe should have split it up - oh well.  Thanks for the help.

[NixVegaGT]

I, for one, love the combination you've landed on. I'd considered using the 4.2 crank but I couldn't find any laying about when I got to that phase of the build and ended up with the old standard, 300 crank.

The valve length is an issue with bigger valves because there aren't any that are the right length. Most are too long when compared to the stock valve length. I'm using Buick Stage I V6 valves. They are 1.73 in and 1.5 ex. but are about 120 thou longer than stock. That worked out well for my more aggressive cam lift of .544 though. The idea is that with higher lift you need the rocker to angle back more to split the difference in the lift from the stock location. That way the rocker stays more central to the valve head while being actuated. Either way you are going to need to order different rods because the rockers are nonadjustable.

I had actually already setup the heads for bigger valves based on an article by Dan LaGrou. I used Pontiac Iron Duke intakes (1.72) and VW flat 1600 exhaust (1.495). That coupled with single SBC springs. Worked out great with the lift of .488 from the cam I originally picked. Now those parts are just laying around my shop looking all shiny and never used. LOL! If you decide to go bigger valves I'll send you these for a good price. Here's a link to my head page with some pix:

http://www.cardomain.com/ride/2357894/2

From what I understand these engines like tight LSAs. My Erson cam from Woody (the Wedge Shop) is at 108º so, if I was going to pick between the Isky cams, I'm liking the 282 (109º). It might be worthwhile to have Dan Jones run the stats and see what should be used to operate optimally. The rod ratio is the caveat here. 1.98! WOW. That's pretty much just under the stock 2.02 of the 215/3.5. Otherwise I'd just post the results for my engine. My rod ratio is about 1.68 (3.74 bore x 3.4 stroke). Dan?

[cfarmer]

Thanks Nic.  

I have the VW type IV and Iron Duke valves on my valve "options" list.  I was hoping to find a domestic source of larger valves in order to use the stock seats in the 3.9 heads - I thought maybe someone had used the early (75-78) buick 231 valves at 1.625 and 1.425.  But with the length at 4.675/4.698, I guess they're just too tall.  I've been researching the rocker geometry changes with valve lift, hoping to find a rule of thumb on pushrod or valve length changes based on cam lift.  Ever heard of anything like that?

[NixVegaGT]

No, but I was thinking that if the stock height is optimal then as lift goes up, I figured split the diff and increase valve length proportionally. In my case I'm about 150 thou bigger in lift so I should go something like 80 longer, right? I'm a bit over that at like 115 or something. One factor is the roller rockers I'm using give me some margin as well. We'll see how it turns out. I'm due to get my lifters in from TA with a test rod to determine length.

[castlesid]

Cliff,

I built a very similar spec engine last year which I have only recently installed in my MGBGT V8 conversion.

The engine used the same 3.9 block and 77mm (4.2L) crank, Be aware that the stroke is usually a bit shorter than the suggested 77mm.  The Land Rover engine spec sheets give a tolerance of 76.222 - 76.759 or 3.00" _ 3.020" so a little extra machining of the deck heights will be required to optimise your finished deck height.

The bore size of 3.736 + 2thou for clearance is at about the max recommended overbore for the rover block.

I used a custom set of chevy style 5.85" rods which take standard Rover/Buick 215 shells and as I was using a pair of Buick 300 alloy heads modified to reduce the chambers to 48cc and fitted with wasted stem 1.63" Inlets and 1.4" exhaust valve together with the usual mods to the seat areas and bowls, which needed as near as possible a flat top piston.

In the end I opted for a KB143 which have 5cc cut outs and a compression height of 1.561" but as you are probably using the smaller 36cc chambered heads will need a piston with a dish.

I also used a Crower 50232 cam with a set Crane Hi-Rev lifters with the valve gear optimised and ended up using a set of adjustable pushrods although I am not particularly impressed with them

The engine at present is topped of with an Edelbrock Performer .manilfold and Edelbrock 500 carb MGRV8 exhaust headers and single box system which is a bit loud!

First impressions are very good and over last weekend I recalibrated the carb and fitted a set of silver step up springs to take into account the problem of low vacuum at idle from the wide overlap cam.

The engine runs very well and will now idle smoothly at 1000 RPM or possibly less which is better than expected.

Hope thats a help,

Kevin Jackson.

[castlesid]

Cliff.

Forgot to add pictures



Kevin

[castlesid]

Cliff,

Also forgot to mention that the Rover head gaskets will work well and you can choose between the composite 46 thou and tin 18thou compressed thickness to fine tune the compression ratio, there is approx .5/1 difference between the tin and comp gaskets.

The Holley 600 may be a little on the large size for what will be a 4350cc engine but no doubt others will be able to advise.

Kevin.

[NixVegaGT]

Very cool engine, Kevin. I love the combo. WHERE DID YOU GET THAT SUMP? That looks like it holds more than the stock 215/300 sump by a quart. Is it like stock Rover or something? Thanks in advance.

I wouldn't worry too much about the carb size. You can make bigger carbs run. It's all in the jetting. The only concern comes from low end throttle response. I'm using a 600 as well but I've got another 600ish cc's on you too.

[castlesid]

Nix,

Thanks for your comments, the sump shown in the pic is a standard 3.9 R/Rover item but I actually used the original SD1 sump for fitment into the B, I also have an oil cooler so should be plenty of capacity at around 5.5 Litres.

The next development is to fit an EFI system, the new engine is fitted with a 36-1 trigger wheel on the rear of the crank pulley, the bracket and sensor is fitted and I had bungs welded into the collectors for a pair of wide band sensors.

I also have most of the kit to make it run, including a megasquirt MS2 V3 ECU,and the EFI Manifold, trumpet base, Plenum and injectors from 4.0 Range Rover and just need the wasted spark coil packs and leads new high pressure fuel pump, a swirl pot and return pipe for the fuel. I will need to swap the 4.0 plenum for a 3.9 version for clearance reasons.

Having done some research it appears that the standard injectors if run with a 3 Bar regulator will flow sufficient fuel for 285BHP which is a little more than my expectation.

Kevin.

[cfarmer]

Kevin -

Thanks for the great information.  I had seen some of the specs on your buildup on another thread and knew it was close to mine.  The info on the 4.2 crank is especially interesting.  It will slightly change my plans - I'll probably go with the tin 0.018 head gasket to keep the quench area in the right range.  I hope I won't have detonation problems as that will push my CR up to a little over 11:1, depending on the actual stroke.  Also, I've just about decided on the 1.63/1.40 valves - can you (or anyone else) recommend one of the UK vendors?  In any case, glad to hear that your combination is working out...

Nic -

I had also looked through you buildup gallery which turned me on the the Harland Sharp rockers.  Just got a quote from them for $450.  Did you use buick shafts and springs, or get spacers and a beefier shaft?  I believe I saw that you were also using stands with the end supports from someone???   Don't think I ever saw a picture of the completed heads with the rockers installed...

[castlesid]

Cliff,

Just did a quick calculate and with your proposed rod and piston combo, the piston will be down the bore approx 40 thou. at TDC. You will need to do a test build with a piston at each corner and measure the deck heights to be certain before doing any machining.

If you had the decks machined to bring the pistons to 20 thou at TDC this would give a comp ratio of 11.46/1 with tins or 10,54/1 with composites which may be a better solution depending on your intended use. The difference surprised me but of course I have large chamber heads and the gasket thickness has less effect.

Re parts you can obviously get most items from the US suppliers, my pistons came from Summit at a very good price and I'm not sure the 1.63 and 1.4 valves are not sourced form the US as well, TA may be able to help or have a word with D & D

As you are aware the Chevy rod will need narrowing at the big end as will the bearings as the Rover/Buick items will not work with the chevy rods.

Sources for parts in the UK I would suggest Real Steel and V8 Tuner.

http://www.realsteel.co.uk/section1.pdf

http://www.v8tuner.co.uk/

Kevin.

[BlownMGB-V8]

Cliff, what CR you can get away with will depend a lot on what cam you are planning to run. More duration gives a shorter effective stroke and therefore a lower dynamic compression ratio. It's something you might want to consider at this stage of your build.

Jim

[castlesid]

Jim.

Good point about the cam effect on compression below about 3500 RPM and it's a slight problem on my engine with the 300 heads.

My calculated CR is only 9.4/1 with the comp gaskets and the dynamic? CR is only about 8.6/1 so how high is it safe to go using ordinary premium fuel?

We do have Shell V Max or BP Ultimate available, at nearly £5.00per Imp gallon in the uk, and they are reckoned to be OK up to approx 10.75/1

Regards, and great work on the big block beast.

Kevin.

[BlownMGB-V8]

I'd guess that's right on the borderline Kevin, but a lot depends on the characteristics of the engine itself so there's likely to be a lot of variation between engine families and I don't know exactly where the Rover sits on that spectrum. Certainly I'd expect the aluminum heads to help. Anyway check out this link and the associated pages:  http://www.empirenet.com/pkelley2/DynamicCR.html
It's about the most detailed info on DCR I've found so far.

Jim

[NixVegaGT]

I was just about to mention DCR. Thanks Jim. Makes a big difference. Here's an example:

On  my engine I was originally planning on the Crower 50232. Wide LSA. 112º. The intake closes 35º ABDC. My new Erson cam choice closes 71º ABDC. The difference is huge for static vs. dynamic CR.

CR: 12.5:1

DCR (Crower): 11.56:1
really not usable.

DCR (Erson): 9.19:1
Still way to high for regular petrol. Good for E85.

I'm with Jim, 8.6:1 is right at the top end for 91 octane but you may be fine with the aluminum engine. You could also warm up the cam a little more. Just a touch.

[castlesid]

Regular fuel over here is 95RON which I believe is different to your MON? rating and the the two figures may not be that different interms of octane rating.

I have just recalibrated the Edelbrock 500 and the car is now much better behaved, i've got the idle down to a smooth 1000 RPM and it might go a bit lower.

The drivabilty on the road is what really impresssed me, I was expecting the engine to be some what reluctant at low RPM with the Crower 50232 and the Big valve big port Buick 300 heads.

 Surprisingly I could drve at 35MPH in 4th gear at 1500 RPM completely smoothly and it was quite happy to accelerate without changing down, however drop it down to second and hit the loud pedal and it just wants to rev, seem to have the best of both worlds, so very happy.

I appreciate and respect what Dan Jones said a while back, in that the Crower 50232 cam may not be the best for power but the all round drivability has the edge here, especially as I live in a high density high traffic area and I have to drive for half an hour to find any quieter country type roads to enjoy.

I will be running it on the strip in the near future, once i've got a few more miles on it and changed the oil and filter, and then I can find out what the top ends like.

Kevin.

[cfarmer]

Yeah, I agree I need to rethink this and do some work calculating the DCR.  I've got a spreadsheet I put together for evaluating cranks, rods, pistons, heads, etc. for static compression and the quench distance.  I think I can just add the equations from the link in Jim's post, and play around with everything based on the Isky 282 cam.  I may need to back down to 5.85" rods, deck the block a little, choose different pistons, and look at the Buick 300 heads with their larger chambers (there's a pair on ebay right now).

WRT octane, we have 93 readily available in my area (my son runs it exclusively in his Trans Am) and I was planning on that as well.  It's relatively cheap at Wal-Mart and Sam's Club - living next door to the refineries is good and bad.  I wonder what DCR I could get away with based on 93?

[BlownMGB-V8]

Keep in mind that it's only a tool and an imperfect one at that. The DCR calculator has no provisions for different areas under the curve and it's still way better to have a talk with a knowledgeable cam grinder. What it can do is get you in the ballpark, but it's not the whole game by a long ways.

Jim

[NixVegaGT]

Good point. To be more specific the DCR is really just the math at no RPM. As the fluid dynamics of air kick in the CR changes through the whole RPM range.

You may be just fine, Kevin. I'm thinking you may have it dialed in right where it should be considering the aluminum construction and 95 RON. We use PON as the rating. It's the average of RON and MON. It's nice to have it because the difference between RON and MON can vary quite a bit. In other words you could get 95 RON one day that's the equivalent of 91 PON the next it's more like 89 PON. That's extreme but you get the drift.

[castlesid]

Nix/Jim

I must admit I find this static to dynamic C/R subject a bit confusing and although the dynamic ratio may be correct mathematically, the whole point of more overlap is to get a higher density charge into the engine once "on the cam" and therefore you would expect the actual compression figure to rise to potentially more the the original static figure otherwise the engine wouldn't make more power, so what would be the point of a high overlap cam in the first place.

Kevin.

[BlownMGB-V8]

Yeah, crazy ain't it? Lots of people have tried lots of different ways to define what is happening in the process, but when you're dealing with starting and stopping the flow of gas at a wide range of speeds the way we are here, good luck defining it with a mathematical formula. What is true at one speed is just going to be bass ackards at another. I think the DCR is primarily useful for figuring out if your engine is going to ping at low speeds, and as speed increases cylinder filling gets less and less effective. It's simple really, with a given orifice and a given pressure, volume is dependent on time. Less time, less volume. So as the engine speeds up cylinder filling is less effective. Tuning the system for a particular speed makes it more effective in that range, but it's the number of firing cycles, not the amount of cylinder filling that gives the increase in power.

How's that sound for a really simplified seat-of-the-pants explanation?

Jim

[castlesid]

Jim,

So we tune engines to run at high RPM which is less efficient, I think I'll go and have a lie down,(smile)

Kevin.

[NixVegaGT]

LOL. Sort of. It can be, technically, MORE efficient. Definitely less economical though. The thing is as air speeds up it acts more and more hydraulic. So the inertia of the gas column will want to continue to go in the direction it has accelerated to go. SO as engine speed goes up you can close the valve later in the revolution where the piston is actually starting to go back up the cylinder. As RPM goes up this effect can be used more effectively so the later the intake needs to close. This is all to counter the effect Jim is talking about, the increasing difficulty in filling a cylinder quickly. If the cam is tuned right you can actually get MORE than the volume of the cylinder into the engine (theoretically). By using the gas inertia leaving the cylinder out the exhaust port (overlap) to get the charge started in from the intake better. Then the inertia continues as the piston rises getting more volume into the cylinder. Pretty interesting.

It works awesome at the RPM it's tuned for but not as good for the RPM it's not. The closer you are to that RPM the better. That's where the problems start at low speed operation. The engine needs higher compression to offset the reduction in actual volume of the cylinder due to this modification. Let's work through an example:

I've got a cam that opens the intake at 35º BTDC and closes 71º ABDC. SO at low speed the cam pushes the charge up into the intake then pulls it down into the cylinder then pushes part of the volume out the exhaust. SO since I have less volume if the CR is at, lets say 9.5:1, it would actually be around 7:1. NOT GOOD! Especially for ethanol. I set my CR to 12.5:1 which gives me a CR of about 9.2:1 at idle. That will translate to better manners at low speed operation. This is why your engine runs well at low RPM even with a "performance" cam. BUT yes this effect also pumps a bunch of unused charge out the exhaust so, yeah, less economical. No doubt. LOL.

[BlownMGB-V8]

And then just to make things even more fun, wonder what happens when you throttle the intake? Obviously effective compression goes WAY down, since only a small fraction of the cylinder volume actually ever gets there. With a lot of overlap, wouldn't this effectively create an EGR effect? (So why did we ever need EGR in the first place?) Lots of exhaust gasses getting swished around in there, not all that much going out the tailpipe.

Think your head hurt before? ;-)

Jim

[NixVegaGT]

Kevin,

Something occurred to me while researching cam timing. If you are having trouble with the 8.6:1 DCR. You could retard the cam timing a couple degrees. Maybe even as little as 1º would do it.

Just thinking out loud.