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Dual Plenum Intake Manifold

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143K views 140 replies 34 participants last post by  Tid  
#1 ·
Been seeing these pop up on a couple different sites for Forced Induction applications.

Basic idea is that they provide balanced cylinder filling, but for the K-series they would serve double duty by allowing us to run the throttle body facing the opposite direction, ideal for charge pipe routing.

Taken from http://www.bufkinengineering.com/
When Audi introduced the 20V motor. The car was homologated with a unique special cast intake manifold with a dual plenum. One drawback of using a single intake plenum is that after the charge air passes through the throttle body, the pressurized air isn't going to hit the runners going to the head equally. Runners closer to the front near the throttle body could very easily get more air than the cylinder furthest away. The Air velocity could play a factor in this as well. Its a very different concept when compared against a normally aspirated car where each cylinder's vacuum draws air into the cylinder so a vacuous single plenum with velocity stacks makes alot of sense. Also on a normally aspirated car, its very common to see individual throttle bodies for each cylinder to get maximum airflow with the least pressure resistance. So how does one actually design an intake manifold that allows or at least attempts to provide equal airflow to each cylinder? Well why would one even want to? If modern electronics allows a different fuel injector pulse to each cylinder, we could just adjust the fuel flow to compensate for the difference in airflow. We could do that, but does that actually give us the most efficient use of the engine's potential? Surely if one cylinder is drawing in 50 cfm of air and another is drawing in 40 cfm, the ideal thing is to get each cylinder to take 50 cfm of air. More air means more fuel and that means more power. So in a perfect engine each cylinder gets an equal amount of air. Having one cylinder running rich or lean from unequal airflow could lead to premature engine failure. So simply put. Dual plenum intake manifolds are turbocharged version of individual throttle bodies...
....Its also characterized by its large 2nd plenum which sits over the primary plenum underneath. The primary lower plenum with connects to the throttlebody is gradually tapered like a cone with a continuous single vent slot that allows gas to pass into the 2nd plenum. The 2nd plenum acts as a collector which then feeds the runners to the head. Pressure in the 2nd plenum is equallized since its not effected by gas velocity and inertia or the pressure variation from front to back of the 1st plenum. Since flow equals velocity times area. The reduction in flow which is released through the side slot is equal to the reduction in area of the plenum assuming velocity is constant. So a smooth conical taper with establish equal pressure and air distribution into the 2nd plenum.
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Ok, basic idea sounds good. Now some pics.

1985 Pike's Peak cars and Audi Group B S1 Evo 2 had these versions fitted:

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Audi R8 Le Mans car

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Manifolds made by Lehmann Motoren in Liechtenstein

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Another example

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Discussion starter · #4 ·
They don't work for NA engines.
Space constraints is a non issue, the conical plenum can be mounted underneath the original plenum.
Look at the curve, the peak numbers mean nothing. Power comes on earlier. The only change on the toyota motor was the intake manifold.
 
Discussion starter · #8 · (Edited)
Discussion starter · #11 ·
drtye said:
We have them at work... I dunno, theres alot of trouble with them. They do work but they gum up and stick, then your doing a manifold replacement (in the dealership).... They can be a headache...
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How are the PCV systems ran?
Are the turbo seals leaking at all?
Interested in seeing pics if you can snap them, and the cars they are on...guessing V12 bi-turbo saloons :silly:
 
Discussion starter · #17 ·
allmotorcoupe said:
TWM also makes roller throttle bodies for the K, however they are not exactly cost effective haha.

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Oh yeah, forgot about those.

Are people running ITBs on turbo'd setups now? Interested to see how it benefited cylinder/cylinder EGTs.

Figured that this design may be beneficial to some of the guys out here, certainly seems to work well, and it can be fabbed up for a reasonably cheap price. A quick search will bring up a company that sells the conical 'under' plenum that the throttle body will bolt to. Could probably graft it to the RRC for a prelim test on a turbo'd motor...and then go to a full custom manifold after that.
 
Discussion starter · #19 ·
drtye said:
Puke, i want to run an rrc, then slap a cone onto it and see the difference (if any)
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http://www.jasperintegration.com/navi.html
This is the site I found with the cone. I like the idea of having the throttle body facing the opposite direction for optimized intercooler pipe routing, only thing I am not sure about is how the accessories will fit into the mix. Might be a little tight for some applications with the motor closer to the radiator.
 
Discussion starter · #22 ·
ecko01 said:
The only one of the pictured manifolds that was done correctly was the factory Audi setup where the laminar distribution chambers (not dual plenums) wrapped all the way around both sides of the plenum chamber. The thing you guys seem to be unaware of is that fluids don't flow into tubular holes from the top. The flow is around the periphery of the hole. This is the reason all air intakes benefit from the use of "velocity stacks", since the radius below the horizon allows the fluid to flow into the tube smoothly. A manifold that only has a laminar distribution chamber on one side of the plenum was built by someone who doesn't understand airflow!!!
Click to expand...
Did you read the linked thread?
http://www.mr2oc.com/showthread.php?t=403005

The guy has "velocity stacks" on each runner. Gains were made, turbo spooled faster. Looks like it works to me.

Have you tested these types of manifolds before?
 
Discussion starter · #29 · (Edited)
rbsjnh said:
question is how big do I make the plenums?

snd which chamber do I run the c.s.v off of, Im gonna guess the plenum closest to the runners
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CSV? Temp sensor?

I don't see this being used with a roots type SC.

A centrifugal SC, or turbo setup, yes.

Most of my research has concluded that OEM plenums are compromises, usually for space.
For NA applications:
Larger plenum results in more power, but slower response to throttle input.
Smaller plenum results in less power, but quicker response to throttle input.

This 'dual' plenum is more for evening out the cylinder/cylinder variances in air mass and pressure.

Rich, check out these threads, they touch on plenum sizes and Roots type SC systems.
http://www.eng-tips.com/viewthread.cfm?qid=88498&page=78



Here is my thinking...
If the OEM 2.0L is making 200hp NA, then I would say it ingests 0.5L of air per cylinder to make that power.
The air is being pulled by the vacuum of the motor, so it is not filling the plenum very efficiently.
Going larger will facilitate the lack of filling ability of the engine vacuum...

On an FI app the air in the plenum is pressurized and if the Turbo or SC can fill the plenum fast enough, then it only needs to be that large. We run into issues when the motor is out running the turbo or SC.

There is a reason this is in the 'theory section' :D

Luckily for me, there are a ton of great dyno plots on the site for different turbo apps using an RBC manifold. Good place to start right there for determining what turbo I want to use. Adding a conical plenum to an RBC on one of these plotted motors would be an interesting test, and would show us how well the RBC is at distributing pressurized air to the different cylinders.
 
Discussion starter · #30 ·
kr4win said:
more than that,the car made 20hp more at 4500rmp :wow:
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drtye said:
Yea, your not the only one to see that.
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Yeah, it goes back to balancing the motor.
We can balance the static weights of the components easily, but balancing out the air flow, fuel, EGT, etc across the cylinders is difficult to do.
The easiest/best way to start is by metering the airflow.
 
Discussion starter · #32 ·
rbsjnh said:
Compressor surge valve...think wastegate
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Anywhere between the throttle plate and the compressor I would assume, not sure how you will be routing your app yet.....
I will probably mount mine on the side of the intercooler, above or below the exit pipe (depending on how the pipe is routed).
 
Discussion starter · #41 ·
Crimson_Marquis said:
Damn.

Now I'm curious as all hell.


Don't mean to get off topic here, but.....The whole.....ITB's in a plenum thing is throwing me off. Anyone speculate how well that mani would work on an FI setup? Or is that just an N/A thing strictly?

Not sure I understand the reasoning behind this design.
Click to expand...
Those are not ITBs. It is a single throttle plate manifold with conical trumpets inside, like the OEM.

These are air boxes for ITBs
http://k20a.org/forum/showthread.php?t=76939
http://k20a.org/forum/showthread.php?t=43478

The closer the throttle plates are to the ports the more immediate the throttle response. This is the idea behind BMW and Nissan using these ITB/turbo systems on their gran touring cars.

What I am looking for with the dual plenum is even distribution of the air to each port. Throttle response will be the same as if I were to use an RBC or the Kinsler manifold.
 
Discussion starter · #44 ·
Crimson_Marquis said:
Ahhh.

Yeah, you're right - trumpets vs. ITB's. Thanks for the links, Sig.

If you're wanting dual plenum....then two separate manifolds with one (x1 ea) TB? Or one mani, one TB that splits 1-2-4? How are you envisioning an optimal IM for your engine/yourself? It seems as if you've done alot of research on the subject, considered all the ones listed and still not content with what you're seeing. Just an observation.
Click to expand...
Just one throttle body. The first plenum feeds the second, which feeds the runners.
The idea is to use the two plenums as a flow filter, to meter the air to each cylinder equally. On a turbo application where pressure can over come the less than ideal flow properties, I think that it will show some benefits over just using the RBC or RRC.
The dyno plots in the MR2 thread I linked back up this idea, as the difference between the two plots is the second plenum. An added benefit of this design is the ability to mount the throttle body facing the opposite direction, improving intercooler efficiency and piping design.
 
Discussion starter · #47 ·
Something like this?
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If space is not a constraint, then I would make the runners as straight to the port as possible. They should be an extension of the port, the air should not know that there is a transition. Like so:

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See this thread, it has some conceptual and CFD analysis of the dual plenum manifold:
http://forums.hybridz.org/index.php?showtopic=61549
 
Discussion starter · #48 ·
The thread I linked at the bottom of my last post, great info in it! :up:

Some more eye candy:

HKS built 4G63

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This is similar to what my idea was for the K-series. I would have the conical plenum on the underside of the main plenum.

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