custom plenum and fuel rail on Rover EFI manifold

[BlownMGB-V8]

Curtis, the runners are very likely to be different lengths and also different volumes. The ports in the head should be pretty close to equal volume although some minor variation is likely. So your task is basically to equalize the overall volume of the ports and runners by trimming the trumpets. You should be OK in disregarding the ports when you do this but if you can check with Dan Jones he will have the exact answers you are looking for since he has done a lot of port work on these heads.

Sticking with the full set of injectors is the safest approach, short of more thorough testing and I think you will be fine doing that. Your flow test after cleaning gives sterling numbers and there is no reason to think partial flow would show any more spread. But when you start tuning just remember that it can happen and be aware of any inconsistencies from one side to the other.

Jim

[ex-tyke]

Equalizing port/runner volumes wouldn't necessarily guarantee equal flow. If you're trying to qualify equal intake runner flow, wouldn't a flow bench test be you're best bet?....ie tune the trumpets for equal flow.

[BlownMGB-V8]

That would be ideal, if he could get set up with the same head he is using. Same valves would be even better. A change in the bell shape can also vary the flow, and it should be tuned at different flow rates to see if they can be equalized under part throttle conditions. He already has some pretty good tri-Y headers so exhaust flow should be pretty close to equal. Curtis, I think once you are finished with this you are going to be pleasantly surprised with the output of this engine.

Jim

[Moderator]

I'm definitely a neophyte in all this... but my impression is that a flow bench is the right tool for optimizing and equalizing max flow rate but isn't all that useful for working out Helmholtz (pressure wave) resonance effects. (As the intake valve opens and closes very rapidly, pulses of pressure run through the air column in the intake track...) Am I right in that assessment?  I certainly do wish I had access to a flow bench, and to someone who could show me how to use it!  I'm sure it would be helpful, but I suspect it would only help with part of the puzzle.

My plenum top will be held on by just two cap screws, I have an extra set of Rover trumpets, and Rover trumpets are only ever held in by friction... so trial-and-error dyno testing is feasible. It would for example be easy to do a quick-and-dirty A-B comparison between staggered (equalized port volume) and max-length (100mm) trumpets in consecutive rolling-road dyno pulls. If conventional theories hold true, staggered trumpets should produce a higher peak torque whereas max-length trumpets might produce a flatter curve with peak torque at a lower engine speed.

My machinist friend and I have talked about spinning some full radius trumpets out of aluminum tube. I enjoy few things more than learning new manufacturing processes! If there's a ready market for them and if I could take some pre-orders...

[mgb260]

Curtis, Bill on the SAOCA used equal length runners on a homemade intake. Shorter length moved powerband up,longer length helped low end torque.

[BlownMGB-V8]

Yeah, they had those BBC's (Can AM maybe) with the staggered length runners supposedly to broaden the torque curve? Seems I heard something about that.

Maybe as much worth considering as trumpet length is proximity. What I mean is those runners nearest in the firing order really should be separated in physical location. #5 and 7 are usually the biggest concern but where the runners come together in the center like these do the 4&3 pair and the 6&5 pair might be considered as well. The problem is one cylinder stealing the charge from the adjacent one and it was a real problem in the early flathead V8 engines, leading to extremely and unexpectedly low power outputs until the dual plane type intakes were developed, which explains where this seemingly odd V8 design came from. I do not really know how severe the problem is with EFI where you are not dealing with the fuel but the cylinder is sucking in air for close to 180 degrees and the runners are 90 degrees apart so it is at least worth looking at where the runners come out to see how much separation there is on those three pairs. I've never done this and I would expect them to be optimized but I've been surprised before.

On the resonances, again there will be some interplay between the runners and without having the valves slamming shut there is no way to evaluate it that I know of. Sometimes with IR intakes you could see liquid fuel at the top of the throttle bores where it had been carried by the reversion but without some extremely elaborate test equipment I'm not sure how you would measure this. Possibly some sort of orifice equipped accumulating manometer sensitive enough to measure a decrease in pressure in the runner, or possibly a differential from one end to the other. It would seem that a larger than average differential would indicate reversion. But then the question is, how much difference does it make and then what can be done about it? Without more information I don't have any answers for that.

Jim

[Moderator]

Next I'll take the plenum back to the expert welders at Peterson Fluid Systems and have them weld on bosses I've made for PCV, MAP, and vacuum advance connections.

I can't say enough about how pleased I am with the job Peterson Fluid Systems did on the welding. Of course their main business is dry sump oil pumps, tanks, breathers, filters, lines, fittings, and other lubrication system components... but they're happy to take occasional welding odd-jobs too. Give them a call.


(Did I mention that they're a BritishRacecar.com advertiser? Tell them I sent you!)

[Moderator]

Something else to report: I did a little cc'ing this morning to satisfy my curiosity. I only had rudimentary tools at hand but I measured everything twice and seemed to get consistent results.

The four intake ports on a spare Buick 215 head are indeed very nearly identical in volume. The number I got was ~90cc each.

The Rover EFI manifold really is symmetrical. Mine has been decked 1/2" on top. I measured: cylinders #1 and #8 ==> ~190cc, #2 and #7 ==> ~160cc, #3, #4, #5 & #6 ==> ~130cc.

The volume of a stock (100mm) trumpet is easy to calculate: just barely over 114cc.

Thus, if I trim trumpets to equalize volume, the four in the middle will end up ~25mm longer than the ones for cylinders #2 and #7 and ~50mm longer than the ones for cylinders #1 and #8.

[Moderator]

Now we have a very stout and tight fitting plenum lid. Scott McRoberts does handsome work, doesn't he! The photo above is just a trial installation. Tomorrow we'll radius the lid's outer edge. I'm not sure if we'll stop with that or machine-in a little bit more detail. I expect the lid will ultimately be powdercoated satin black to match the valve covers.

[rficalora]

If it works as good as it looks you'll be taking orders before you know it!

[BlownMGB-V8]

That's pretty sharp Curtis. What does your clearance over your trumpets look like?

Jim

[Moderator]

Thanks, guys!

We finished the lid this morning. After sleeping on it, I decided to cut a shallow 3/4" racing stripe down the top from front to rear, off-center to driver's side like the big white stripe on my roof. We flipped the cover over and cut out the bottom so it's 1/8" thick through the center.

So my next question is: "How much clearance between trumpets and lid do I need?" The front edge of cylinder number three's trumpet will be closest. Without trimming it's only got about 3/8" clearance. That probably isn't enough, so each trumpet will need trimming after all. Maybe 3/8" off each? (More get trimmed on #'s 1,2,7,&8 to equalize runner volumes, per previous posts.) For a reality check, I pulled out a Rover 3.9 plenum and measured its trumpet clearances. Stock, they had ~0.45" for cylinders 2&7, and ~0.55" for cylinders 3&5.

[BlownMGB-V8]

Best way to determine that would be with a flow bench and the lid is going to affect #3 somewhat. You could probably trim it a bit more than the others. The torroid formed between the lip of the bell mouth and the lid effectively extends the length of the tube, provided the cross section is correct. What you can do is determine the area of the cylinder from the lip up to the lid (taking into account the lid angle) and compare that to the area at the max diameter of the flare. Where the two match is going to be real close to the smoothest transition at minimum height, or maximum length of the tube. The angle will probably throw the calculations off a little but at least it'll get you close. See how that matches up to the Rover spec.

Jim

[Moderator]

Newer photos:


(decided to add a "racing stripe")


(Rover intake manifold with thermostat bypass relocated to align with Buick front cover)

[MGBV8]

Ain't that purty!

That GT has come a long way since Annapolis in '98.

[Moderator]

Thanks, Carl!

My MG was pretty well sorted by Annapolis... but your comment made me think back to really early test drives. Here's the earliest snapshot I have of it in "running" condition. (No air cleaner, hood pins, or license plate yet.) That's my momma and one of my sisters borrowing it for a hell ride.  "SEPT 1991" was printed on the back of the photo by the developer.



I guess this topic has pretty much run its course. Hopefully soon I'll have something to post about plumbing, wiring, and electrical components.

[BlownMGB-V8]

Wait Curtis, we want to know your final solution for the trumpet lengths.

Your "racing stripe" looks really good btw. Nice touch. Very classy job all around.

Jim

[MGB-FV8]

Curtis, I'm impressed by the cleanness and the execution of your installation; great job A+

[roverman]

Curtis, regarding the photo, what about the tree ?  Good to see brand loyalty. Cheers, roverman.

[MGB567]

Curtis is there an update to this topic in particular what you ended up doing with trumpet lengths and manifold tracts?

[Moderator]

Wow. It's been awhile already!  

I ended up trimming # 1, 2, 7, and 8 to equalize volume as mentioned earlier in this thread:

Thus, if I trim trumpets to equalize volume, the four in the middle will end up ~25mm longer than the ones for cylinders #2 and #7 and ~50mm longer than the ones for cylinders #1 and #8.

Here's a snapshot with the lid off, after trimming.  I left the middle four 100mm long. You can see here that we milled the bottom side of the lid to get more clearance above them.


Re: manifold tracts... I may have knocked off a little casting flash. My heads aren't ported either. Perhaps one day I'll "flow" the whole system (or have it done.)  Bigger/better exhaust headers sit higher on my to-do list.

Thank you for your interest!

[MGB567]

thanks Curtis. I plan on showing this to my guru. I was looking at just buying from V8developments but they haven't replied just like ACT and SC-Power and V8 tuner just wasn't interested  RPI has nothing in their Ebay shop either so I'll revert to DIY

[donkelly23]

Mine