Well, I've been studying lots of plenums lately as I'm designing an intake manifold to be produced for Audi 5 cylinders.

Part 1: Transition From throttle to Plenum.

From what I can tell you want a smooth transition from the throttle body to your plenum. You want a conical transition to increase the pressure of air entering the plenum. Bernoullo's Equation applies here. As you decrease the velocity of the air charge entering the plenum, you increase the air pressure. Flow travels along pressure gradients, from high pressure to low pressure. Having a high pressure plenum feeding the low pressure runners, air will flows into the runners.

http://en.wikipedia.org/wiki/B...ation
http://www.grc.nasa.gov/WWW/K-....html
http://www.princeton.edu/~asmi....html


Part 2: Plenum Shape to equalize pressure to each runner.

Once you have transitioned from your throttle upto the major size of the plenum, you will want to shape the plenum in such a way to equalize flow to all cylinders. This is accomplished by tappering the plenum from the throttle side down to the last plenum. This is done to keep the same relative velocity, and thus pressure throughout the plenum.

Part 3: Transition from Plenum to runners.

To help promote laminar airflow you want a smooth tranistion from the plenum into the runners. Having a nice radius on the enterance of the runner helps promote laminar flow. Laminar flow = more air flowing into the engine.

http://en.wikipedia.org/wiki/Laminar_flow

Also, having a tappered runner increase laminar flow as it travels down the length of the runner. This can been seen in the Full-Race and AIR intake manifolds.

What more is there to add? I would like some constructive critism on this please

Anaylize this picture to see What I'm talking about. This is also just analyzing the physical design of the intake manifold. I will go more into material selection later on.



Regards,
Justin

 

What more is there to add:

1) How manifold volume effects performance
2) How runner CSA affects torque curve
3) How runner length can produce desirable harmonic effects

 

this is my opinion at the end you can do as much analytical and computational methods as you want to try to find the greatest efficiency of a design but itll never be accurate. even the elitest of companies in the world boeing use navier stokes (its like a grid. 3dimensional differential ****) to calculate viscous flow over a region. and they still say its not accurate and got teams researching alternatives methods blah blah lbah.

when it comes down to it. all that matters is real life testing. an example could be the picture u got endyn cf intake manifold. most intake manifold dont have too much design but this one had it. equal flow through the cylinder and flow number to support mad powa made out of cf to not be as hot vuteverr elseness. but at the end why dont a lot of the all motor drag racer use them? theres a drag racer ive seen that used to use it and then switched to a ported jg hmm. and now im hearing endyn making another intake manifold hmm.

wait so wtf em i tryna say. designing soemthing that works doesnt mean **** real life numbers testing is all that matters. we gotta realize were the buyers not the designers. see how the product peforms in real life and see if it works with your engine goal. wutever mayn jus plan accordingly

 

I agree that you can't design something outright that works the best it can. Modeling what will happen in the real world is hard to do. I'm just trying to point out what the best manifolds out there have in common. Check out Full-races manifold:



It has all of the features that make the AIR a very powerful manifold, and then some.

On runner length you have to look the helmholtz frequency.

http://en.wikipedia.org/wiki/Helmholtz_Resonance

I dont really know how to calculate the proper plenum volume, but if you are looking for a large mass flow, you are going to need a large plenum:




Also look at the AMS Evo manifold. One of the best for the 4g63 It has a large plenum, and provides a nice taper from the throttle into the plenum:
http://forum.vwsport.com/pics/...5.jpg
http://forum.vwsport.com/pics/...6.jpg

 

its all about the "z" tune

 

a roungh guide i use for mani volume is 1.5 times the engine size and it seems to work pretty well

 

Resonance stuff looks impossible over 14.7....

 

Subscribed for knowledgey goodness

 

Hej Justin.

Maybe a german ccompany can help you. Thats where the Audis come from.

On http://www.mft-berlin.de they offer a lot of stuff for that cars. maybe it helps you.

 

This is the current manifold that is available for my audi 5cylinder. I personally think I can design something better then it:

http://www.034motorsport.com/p...d=200


I'm just trying to decide what plenum configuration I'm going to run. I really like this design:


But for good clearance I may go with with something more like this:

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Justin Olson &raquo;</TD></TR><TR><TD CLASS="quote"> I really like this design:


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That is a really nice plenum....big gradual transitions, center inlet, nice taper on the runner.

 

Yeah, I'm having that design built right now actually. I just haven't seen any other do it, so I was worried there was some flaw to it. I guess I'll just go ahead with the plan.

Here are some CAD files I did in Autocad:

 

I think that the reason you dont see many doing it that ways is the amount of space that it takes up. As I recall doesnt the plenum on that particular car peek through the hood?

 

that sketch you made up looks like the angles of the front and back of the plenum looks kinda sharp for cylinders 1 and 5. i'd make it to that there is a little bit of straight to the side wall before making the angle toward the tb. it may help even the flow a bit? i'm probably just talking out my *** again though. just a thought.

 

ever thought about spliting the boost in 2? It wouldnt work for you in 5 cyl but 6 cyl guys do this. You split the boost before in 2 than after in 3 each, this make for n equal distribution and more compact manifold.

 

That design wouldn't work too well for harmonics. Kharmann frequencies occur between the valve and the plenum. If you did a 1-3-6 design it would have differing length runners and almost no real plenum to speak of.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Justin Olson &raquo;</TD></TR><TR><TD CLASS="quote">
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i wouldnt knjow how well that would be for a single throttlebody manifold. i would think it wouldnt because it would have to cut another 90* to the runners.

 

Justin...I used some of those RMR stacks and inlet pipes...you were right about their Inner Diameters...way fucked up. We're going to reorder some 2" inlet tubing and 2" stacks and try again

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ~RTErnie~ &raquo;</TD></TR><TR><TD CLASS="quote">Justin...I used some of those RMR stacks and inlet pipes...you were right about their Inner Diameters...way fucked up. We're going to reorder some 2" inlet tubing and 2" stacks and try again </TD></TR></TABLE>

are you talking to me or justin olsen? i know i quoted about the rmr stacks in a previous thread, wasnt sure if justin has also.

 

He's talking to me. The ross stacks are 1.75" ID. There website says something about a 1.88ID,

 

i was UBER dissapointed. But they'll have to work for now :-P I'll post up pics soon. Ive got some cool **** going on in teh shop

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Justin Olson &raquo;</TD></TR><TR><TD CLASS="quote">He's talking to me. The ross stacks are 1.75" ID. There website says something about a 1.88ID, </TD></TR></TABLE>

mine measured out to 48mm id(1.89") on the flang side. so i guess mine is right. i have no idea why yours are 1.75" (44.5mm) as that is a big difference. thats over 1/8". i think you should call rmr about that. they are easy to work with. i havent had problems with them at all.

 

what is the advantage of using the raised velocity stacks in the plenum. In theory the air on the floor is supposed to move faster, so wouldn't you just want a nice flush, radius'd entrance into the runners thats close to the floor

 

I've read some ideas about tuning runner length... And I really don't care for the practice now. It's hit and miss, you hit one harmonic and gain power and you're creating other nodes which lose you power and create reversion... It makes the powerband peaky... Good for a drone motor or something else you can keep in a narrow RPM range.

Personally, I generally like short runners (so the tuned length is way out of the powerband) And the short, uncomplicated runners make things nice from a standpoint of pumping losses.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by b16hybridsol &raquo;</TD></TR><TR><TD CLASS="quote">what is the advantage of using the raised velocity stacks in the plenum. In theory the air on the floor is supposed to move faster, so wouldn't you just want a nice flush, radius'd entrance into the runners thats close to the floor</TD></TR></TABLE>

Wrong theory. Because of friction the air directly adjacent to the wall is not moving, and the velocity profile is parabolic outward from the wall until it reaches stream velocity. This is called the boundry layer. The point of the raised stacks is to get the inlet out of the boundry layer.