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Intake manifold design resources?

Intake manifold design resources?

(OP)
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!

RE: Intake manifold design resources?

With a blower, the importance of the intake manifold reduces to mere ductwork. Yeah, there might be 5 or even 10 percent available there, but it will be masked by the 20 ... 100+ percent increase over n/a provided by the blower.

Any number of hotrod sources will show and tell and occasionally prove how to make better manifolds for naturally aspirated engines. ... but they all tend to increase the internal volume and external bulk of the manifold, whereas the usual biggest problem with a blower is getting the blower, intercooler, and ducting within the vehicle's envelope. The intake manifold is therefore reduced to vestigiality in the interest of packaging.

Coupla flanges in the proper place, run tubing between them nicely, and go on to the next challenge.

Mike Halloran
Pembroke Pines, FL, USA

RE: Intake manifold design resources?

carb or fuel injection?

RE: Intake manifold design resources?

... and what type of engine/cylinder configuration.

A lot of intake manifolds nowadays incorporate an air-to-coolant intercooler inside them. Getting intercooling trumps being able to tune the runner lengths when the supercharger is stuffing air into the engine anyhow.

RE: Intake manifold design resources?

(OP)
It will be a fuel injected V6 application. Single turbo.

I've researched a few things online and there is obviously great information out there. However, I was hoping for a more comprehensive collection in the form of a good book or two.

Although the duct work is one of the main challenges, I've still read about poor manifold designs causing lean/rich conditions in the different cylinders due to uneven distribution of the intake flow. I'd like to learn about some of the smaller details as well such as the effect of port shape/location on flow efficiency and pressure/velocity drop.

Thanks guys!

RE: Intake manifold design resources?

If you are using multi-point fuel injection (which you should), the old school wet-flow issues leading to poor cylinder-to-cylinder distribution are nonexistent because the manifold is dry inside and the injector is right at the intake port.

RE: Intake manifold design resources?

BrianPetersen - but if all injectors injects same amount of fuel, and manifold is poor designed, can't be, that in one runner will be more or less air flow than in other? :)

RE: Intake manifold design resources?

The manifold would have to be very badly designed indeed to have that much flow asymmetry. The turbo will stuff in more air than is needed by any cylinder. The manifold acts as a revervoir or accumulator for storing pressurized air between valve openings. ... so the manifold geometry is nowhere near as critical as in a naturally aspirated engine.

Additionally, it's possible that a sufficiently adaptive ECU could detect a weak cylinder just from the engine's instantaneous performance, and compensate by adjusting fuel flow to that cylinder. I don't know what such an ECU is in production now, but it's certainly achievable.

Mike Halloran
Pembroke Pines, FL, USA

RE: Intake manifold design resources?

If you have multi point injection, the design aim is a plenum containing near-stagnant air, feeding equal-length runners with bell mouth entry. If the engine has factory MPI try to use the original manifold.

je suis charlie

RE: Intake manifold design resources?

As mentioned before, once you've made the leap from NA to forced induction, all that's been learned about manifold tuning is essentially obsolete. Still fascinating and clever, but then again, so were carburettors. And mechanical fuel pumps.

Manifold internal flows are still interesting for the purposes of EGR distribution, but I doubt that's a problem here.

I wonder how mean fuel delivery varies from injector to injector and if that variation changes with age?

Steve

RE: Intake manifold design resources?

Quote:

The manifold acts as a reservoir or accumulator for storing pressurized air between valve openings. ... so the manifold geometry is nowhere near as critical as in a naturally aspirated engine.

To expand upon this concept, suppose we have a supercharged V8 engine with flow-restricted side-by-side pairs of intake ports.

I've done some tests by removing the divider between the pairs of intake ports as far as possible. On a flow bench, the increased plenum volume increases flow to each cylinder. That's a huge plus beyond what is available with conventional hand porting.

In practice, what will be the effect of a log/plenum intake all the way to the valves? Absolutely no port separation from supercharger to the eight intake valves?

Of course, cam design is a factor. At some point increases in duration and overlap will begin to be a problem with that degree of interconnection.

What other plus/minus factors could be at work?

jack vines

RE: Intake manifold design resources?

(OP)
Thanks for all of the responses guys.

Yes, it is multi-port fuel injection and it was previously a supercharged application. (GM L67 3800 motor). The supercharger was an M90 roots style blower and was therefore taking the place of the plenum.

I have an empty supercharger case that can be used as a plenum, however, the volume is quite small. I can also replace the intake manifold with one from a NA 3800 engine, but again, the volume will be considerably less than what I read is ideal (ratio of 1.6:1 or more compared to the engine displacement). This is what prompted me to look into the custom plenum as well.

As for the unequal distribution of air in the cylinders... My understanding is that the amount of fuel injected will obviously be a function of the amount of air available as read by the MAF and MAP sensors. There are only one of each of these sensors located along the intake tract and the plenum. Therefore if plenum and runner geometry cannot provide equal distribution of air to each cylinder then you can have rich/lean conditions. Or am I over-thinking this?

Intake manifolds like this: http://www.marcellamanifolds.net/images/IMG_0906.j...
are designed such that the incoming air flows into a large volume (expansion) and should slow the velocity of the air such that the front runners are not starved if the air were to otherwise blow past and accumulate towards the rear cylinders.

RE: Intake manifold design resources?

SAE paper 720214 "Design Refinement of Induction and Exhaust Systems Using Steady-State Flow Bench Techniques"

The authors seems to consider flow balancing (naturally) quite separate from mixture distribution, but still important at least for normally aspirated passenger car applications.
" Branch Balancing- During a flow program on an intake manifold, several design parameters can be varied to improve
flow to one cylinder at the expense of another. The following discussions (Angle of Turn at the Branch, Flow Path
Length, and Turning the Corner) are useful tools in this procedure,which moves the design toward a goal of equal flow
capability in each carburetor-to-port flow channel. Ultimately, a decision must be made as to whether some
channels should be arbitrarily restricted in the interest of equal flow. In our work, we have chosen equality of flow in
preference to overall maximization. Our rationale was that a middle range of engine speed existed in which equal airflow
was necessary to provide equal compression pressures and knock behavior. This uniformity would then permit the
highest compression ratio for a given fuel, combustion chamber, and spark advance.
In this same range of engine speeds and above, equal compression pressures would promote the subjective sense of
smooth engine operation near wide-open throttle. In surveying the practice of United States engine manufacturers,
we have noted both approaches, sometimes within one manufacturer's engine models. In one instance, the flow
capability of the poorest cylinder was 86% of that for the best cylinder (case study D).
Angle of Turn at the Branch - The angle through which the induction stream must turn from the longitudinal runner to
the transverse branch of a V8 intake manifold exerts a considerable effect on flow capability (Fig. 25)_
Minimizing and varying this angle is one means toward high and uniform flow.
Flow Path Length - Similarly, modest variations in length of the induction stream produce readily discernible effects on
flow. This is another variable whose influence must be considered."

==============
In the earlier SAE paper 670067 "Mark II - 427 GT Engine Induction System" FORD developed the "medium riser" engine to equal the noble but hard to package "high riser" series after simultaneously improving airflow and maintaining good airflow balance for each. 670067 includes similar development work on the SOHC engine.

RE: Intake manifold design resources?

My previous question about an all-plenum intake reminded me of the opposite design, a plenum at the top of long ram tubes. When turbos began being applied to drag race cars, one of the first I ever saw fed pressure to a large plenum placed on top of 18" individual runner stacks of the Hilborn injection. It ran OK, but was ungainly and prone to pressure leaks. While they were trying to seal pressure in piping designed to operate under vacuum, someone pointed out the turbo boost overcome any wave/ram function and they could do away with the long tubes. Removing the ram tubes with their 32 hose clamps from the intake track made it much easier to seal and no loss of power.

jack vines

RE: Intake manifold design resources?

"ratio of 1.6:1 or more compared to the engine displacement"

I believe that is 1.6 time the displacement of a single cylinder. The stock NA3800 should work fine.

Jack. Long tubes can help fatten the torque curve on a turbo motor. Wave function still applies on boosted engines - look at any top level turbo competition engine. Wave effect is less important on a street or budget race engine where often the boost can be turned up to whatever limit (usually detonation) the engine has.

je suis charlie

RE: Intake manifold design resources?

I can't believe there are people on this forum who could think intake design is any less important for forced induction or that any theories are actually significantly different on forced induction.
All engines run on air pressure and pressure differentials. In a sense all motors are boosted. If they didn't have air pressure they wouldn't run. All a turbo or supercharger is doing is multiplying that pressure.
Plenum volume is still important. Runner lengths and diameters will still effect the performance and in very similar ways to NA.
I will agree with gruntgurus last post in that it may not be worth spending a ton of time or money on a street build. In fact for a street build an OEM NA intake will usually be a great choice for a street boosted build. If you are going to take the time and or money to make something then it better be better than stock and that will take some thought and effort.

As for the OP if this motor ever came NA then unless you plan on a massive build pushing the ragged edge it's quite likely the OEM NA manifold would work quite well. Again general manifold function won't change much between NA and boosted.

There are a couple theories among turbo manifold designs. Stock manifolds will usually be tuned for a broad power curve and decent low end. This should also help with your low end spool.
Then you could design and build a mani with tuned induction in mind. A long runner mani with a focus on low end and quick spool. Or you can go shorter with a focus on broad power curve.
Or you can go super short giving up pretty much any effect of resonant tuning and just trying to maximize all out airflow. This will tend to give you more peak RPM power.
Of course these are all very simplified generalizations and there is a lot of finer theory to understand to even start to implement it with some understanding and hope of having the effect you hope for.
Even then there is still some art to it too. Top performance manifolds aren't made off the first design knowing they will work the best. You would make a few designs based off what you think will be best and then you test those designs and then make some variants of the best of those and test and repeat until you are satisfied that you have reached an acceptable level.
As far as general theory, understanding harmonics and sound waves this book is a great start.
http://www.amazon.com/Scientific-Exhaust-Systems-E...

RE: Intake manifold design resources?

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.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Intake manifold design resources?

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

Mike Halloran
Pembroke Pines, FL, USA

RE: Intake manifold design resources?

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.

RE: Intake manifold design resources?

Greg. The plenum chamber provides a stagnant termination for the runners.

je suis charlie

RE: Intake manifold design resources?

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

RE: Intake manifold design resources?

Quote:

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.


Quote:

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.

Quote:

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.


Quote:

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.

RE: Intake manifold design resources?

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/showthread.php...!!!!!

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?

RE: Intake manifold design resources?

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


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Intake manifold design resources?

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

RE: Intake manifold design resources?

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)
[img http://i.ebayimg.com/00/s/MTA2N1gxNjAw/$(KGrHqZ,!n...]

3SGTE (Turbo)
http://img.photobucket.com/albums/v509/xtcdx/Gen2M...
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.

RE: Intake manifold design resources?

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-result/?author...

PJGD

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