Intake manifold design resources? 2

[dubc4]

Looking to take on an ambitious project and design my own intake manifold for a project I have coming up.

Has anyone come across any good resources for design criteria/considerations for engine intake manifolds? Mine will be specifically for a forced induction application.

Any links would be very much appreciated.

Thank you!

 

[GregLocock]

True dat.

Cheers

Greg Locock


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[SomptingGuy]

Equal length runners may make it sound better. But then again, not much intake noise will get through the compressor anyway. Minor VE tweaks from wave tuning are kind of irrelevant when you can pump the pressure up to the point of destroying your engine already.

Steve

 

[GregLocock]

I was thinking more of equalizing the air mass in each cylinder than acoustics

Cheers

Greg Locock


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[yoshimitsuspeed]

OK show us the money. Let's see some data showing a tuned pipe system with superior performance to a shortest possible direct plumbing solution, both turbocharged.

The reason I'm suspicious that tuned lengths are less important are (1) the turbo provides rather an odd termination, acoustically, so I doubt it'll reflect the waves especially well and (2) skin friction effects will be more important so the gains from resonant forcing are likely to be masked or outweighed by the losses from the longer ducts.

Note that I suspect equal length runners may be worth having, I'm just dubious about the necessity for tuning their lengths.

1. I don't understand what the turbo has to do with runner resonant waves. Those waves will reach the end of the runner, invert and then travel back down the runner. Yeah that will send waves up the intake piping that would be effected by the turbo but that is not going to be a primary influence on a tuned intake.
2. At what absolute pressure would skin friction effects outweigh resonant tuning? Would it just happen to be atmospheric pressure or would it be above atmospheric pressure? If so how would you decide at what point it would become better to run short runners? It couldn't just be when you slap a turbo on.

I would have to do some digging to find any data that was better than internet rumor and I would love to see more solid proof myself but I don't understand exactly what about increasing pressure would do to change the physics so much to simply be able to say that once you add a turbo the game completely changes. On top of that there are a lot of other factors. One big one is actually off boost performance. A manifold aimed to improve low RPM VE will help the turbo spool faster which could be more valuable than a little hit in peak power in some situations.

I'm curious about what pressure/ gas density you'd use to tune said runners.

Pressure isn't very important as it doesn't significantly alter the speed of sound. Temp does so the closer you can get intake temps to ambient the more ideally you could tune a runner for both on boost and off boost. Otherwise you choose the more important one or split the difference to some degree.

If you are an OEM manufacturer - Compare the cost of the fancy tuned-runner intake manifold to the cost of a log manifold but with the turbo boost pressure set 1 or 2 psi higher. Even if it involves making a different compressor wheel to fully "optimize" it.

If there are space constraints under the hood, compare the net benefit of the space-consuming tuned-runner intake manifold and no turbo, to a log manifold but with the turbo sitting where the rest of the intake manifold was.

YES, the wave action is the same regardless of the absolute pressure. It just might not be economically viable or worthwhile to utilize it.

And yet how many OEM turbo cars have log type manifolds? If it really didn't matter why even waste the time, money and materials with a longer manifold yet the vast majority of turbo motors run longer manifolds. Many like the 3SGTE even use TVIS and that has been tested and proven to give a broader power curve.

Equal length runners may make it sound better. But then again, not much intake noise will get through the compressor anyway. Minor VE tweaks from wave tuning are kind of irrelevant when you can pump the pressure up to the point of destroying your engine already.

This reminds me of the people who think putting a turbo rated for double the CFM will actually double the CFM going through the motor even if at the same boost level.

More boost means more heat. It can also move you around the turbo map and since turbos are rarely run on the low side of the islands this almost guarantees you are lowering the efficiency of the turbo which means even more heat. It also means the turbo has to work harder to spin the turbo. On a very efficient system you might get a 1:1 ratio on pre turbine backpressure (PTBP) to intake pressure so on said system if you could drop the intake pressure from 22 PSI to 20 PSI you would also drop the PTBP from 22 to 20 PSI.
On your average OEM turbo you are more likely to see 1.5:1 to 2:1 ratios. The same if you size your turbo small in favor of spool and response. This means that at 22 PSI boost you could have 44 PSI PTBP. Drop the boost 2 PSI on the intake and you drop it 4 PSI on the exhaust. Lower intake temps, less heat to get rid of, most likely a more favorable area of the compressor map and less pressure on the exhaust side would all add up to a notable improvement in efficiency. It could also allow you to run a little more compression or timing at the same boost level making even more power and or gaining even more efficiency.

 

[GregLocock]

Find the data and we'll discuss it.

Cheers

Greg Locock


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[yoshimitsuspeed]

It's very hard to find good usable data on this subject.
Here is one. It shows the low end gains I was talking about using a stock manifold or longer aftermarket manifold. It should be quite possible to tune a longer custom manifold to give better gains across the board than the stock manifold, or at least over the vast majority of the curve. You should also be able to split the difference between those two manifolds for one that gives good solid gains over the stock manifold over most of the curve but it would still make a little less peak than the shorter manifold.

http://www.spracingforum.com/forums...Intake-Manifold-Dyno-Testing-and-Results!!!!!

I think the bigger question should be why would boosted be any different than NA? Even if once boost came on intake manifold length didn't matter that still wouldn't change the fact that off boost VE curve will effect the spool characteristics of the turbo and that can be used to tune the driving characteristics of the car. I still don't see any reason why boosted manifold design, theory or function would be significantly different than NA. As I said, all motors are boosted. A compressor just multiplies that pressure so what makes the difference?

 

[GregLocock]

I think elvis has left the building. Tuned length maybe 100 mm, so first wave would take .2/400 s =0.5 ms, at 6000 rpm consecutive valve events are 20 ms apart

Seems a bit unlikely to me that the tuned length (which frankly that plenum doesn't look like) has anything to do with the performance gains.



Cheers

Greg Locock


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[Lou Scannon]

As we all know (or should) a tuned length runner is a double edged sword, i.e. instead of a relatively flat VE vs RPM characteristic, you get local peaks and valleys.
For that reason alone, I would tend to prefer a short runner, non-tuned intake system for a boosted application. That said, I see no flaw in yoshimitsuspeed's logic.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[yoshimitsuspeed]

I have never heard of a motor that used first wave harmonics. As you say even to hit the first wave at typical redline you would be looking at something like 36 inch runners.
Most manifold designs aim for the second and third harmonics with some effect from the fourth.

As far as that link I expect the stock manifold would be a tuned manifold. The aftermarket one likely has little or no resonant effect. That was my point in posting it. You are comparing a long runner manifold that Toyota likely tuned for good low end and quick spool against an aftermarket manifold that was likely tuned for high RPM max flow.

This takes us back to the point that if runner length did not effect performance in any useful way then why do all OEM turbo cars use runner lengths very similar to their NA counterparts? As short as possible would save space, cost less and be easier to make.

4G63 (turbo)

3SGTE (Turbo)

http://img.photobucket.com/albums/v509/xtcdx/Gen2Manifold1.jpg

Note it also used VVT to help low end and spool.

3SGE Beams (NA)

RB20 (Turbo)

Look at how much room, material and simplicity they could have gained from a short runner mani.

hemi for a performance car I would tend to agree with you but there could be some exceptions. For example if the turbo was big enough to be slow to spool at say 4k RPM you could tune a mani to hit the second or third harmonic at that RPM. This could have a significant impact on spool. If the VE dip was high enough, say 5500 RPM the turbo would still spool pretty fast just because of the increased RPM. It could be worth the gain in spool if you need a broader power curve with quicker boost response.

For a street car for the same reason I would generally also prefer a little gain in low end and spool at the cost of peak power. I believe this is the same tradeoff OEMs are going for.
Most aftermarket turbo manifolds tend to be shorter and focus more on optimized flow.

 

[PJGD]

I find that the presentations (at least those that are directly accessible on the site) in ones' area of interest at the Gamma Technologies Publications page can be a useful resource:

https://www.gtisoft.com/gt-suite/publications/

For the topic of this particular thread, there is not much of direct relevance, nevertheless No. 11 from Magneti-Marelli under the Gas Exchange heading may provide some clues:

https://www.gtisoft.com/publication...65&years[0]&phrase&pagination=1&submit=submit

PJGD