Dual Plenum Intake manifold

[quattro]

In the process of constructing my manifold and i have a question regarding the hole between the 2 plenum's.

What size do you think i should make the hole?

Im currently thinking 450mm x 6mm, ill show you my working out....

2.5" boost pipe (1.6mm wall)

(2.5x2.54)x10=63.5mm

63.5-(1.6x2)=60.3mm (boost pipe I/D)

Do for the surface area of the boost pipe........

3.14x30.15x30.15= 2854.33mm2

and the hole for the 2nd plenum

2854/450=6.34mm

Makes sence?

[Lupo911]

If you do it on CAD, run some Flow Analyses... that will give you some directions , Wall thickness not under 3mm.

In the process of constructing my manifold and i have a question regarding the hole between the 2 plenum's.

What size do you think i should make the hole?

Im currently thinking 450mm x 6mm, ill show you my working out....

2.5" boost pipe (1.6mm wall)

(2.5x2.54)x10=63.5mm

63.5-(1.6x2)=60.3mm (boost pipe I/D)

Do for the surface area of the boost pipe........

3.14x30.15x30.15= 2854.33mm2

and the hole for the 2nd plenum

2854/450=6.34mm

Makes sence?

[JP]

The hole between the two should be no less in cross section than that of the throttle body so it doesn't offer a restriction. Also be wary of trumpet dimensions and the height of them protruding into the secondary plenumb, as the dual plenumb manifolds tend to throw up real uneven flow distribution when not done correctly. Particularly with the middle cylinders favuoring longer trumpets than the outer ones which tends to mess up the harmonics on the runner lengths.
Personally if you know someone that sells a tried and tested one with proven even flow distribution I would buy it rather than make it. There is a good reason why the good ones are expensive.

[quattro]

Fraid i have no CAD software....

RWD19T- Half the fun for me is making my own stuff, I know that Lupo911 sell a very good manifold, as do Repo and Furans but I want to make it my self.
If I try and fail Ill just make a nother one..... As I have the facility and I love doing it I want to..... I'm sure you can apriciate that?
Any Cun* can buy a load of bolt on goodied and say they have built a powerfull car not every Cun* can say they actualy built it!

So what your saying is use the I/D of the throttle body as its slightly larger than the I/D of my boost pipes?

[GazzaG60]

ive done this for the same reason quattro. on the 16v anyway.

i got stacks from jenvey and some plate. used 16v flange, subaru sport mid runners and plate and stacks the rest. never used it but was fun to make for sure.

i just bought one this time round. i looked at the full setup and decided the wagner ic, inlet and xmember were too good not to just get and fit. save custom to an extent.

good look with it. i went single plenum with stacks and a 75mm mustang tb. my mate got it off me and fabbed a fuel rail to fit properly. he was my welding resource in the project.

[quattro]

Not just me then....

Found some pics of the ADU and 3B Inlet manifolds on Motorgeek last night and the difference in flow between each cylinder is quite bad, carstens is good.

As long as I do better than OEM im happy, The 3b max/min flow difference was 12%, and actualy the 3b out flow'd the ADU manifold. Carsten's looks pretty damn good IMO min/max within 4% and totaly out classes OEM.

Look at the ADU one, looks like they got bored after the 3rd cylinder!!!! lol

http://www.motorgeek.com/viewtopic.php?f=18&t=9764

[JP]

All for making ones own manifold, just don't start with a twin plenumb chamber one. There is an art to getting them right as the first and last cylinder will naturally want to flow more than the middle ones. Whereas a non directional plenumb chamber with big volume comparatively speaking and identical trumpets/stacks/runners to each cylinder is guaranteed to give better results for a novice.

But if you are hell bend on dual design the very general rule is make sure the hole flows the same as the throttle body that way you are not introducing an unnecessary restriction. Likewise everything needs to be radiused to minimise turbulence on the transition between the plenums, as the more turbulance you have the worse th throttle response becomes.

[JP]

3-5% is an acceptable variation much more than that and you run into other issues assuming that the exhaust manifold flows evenly ;-)

When I tested the SEM 1.8t intake manifold the percentages dropped below 2% variation on the cylinders and again all it is is one big mildly tapered plenumb chamber with nice radiused entries into the runners. A lot of the flow issues on the stock manifold is not only the guides for the allen key tool but the severe tapering of the plenumb meaning the runners cant pick up flow as evenly from it's full circumference.

So far I've had the privilige of testing 3 different 4cyl dual plenumb intake manifolds from major manufacturers and I wouldn't be happy to put any of them onto a high performance car. Not that they cant be good it's just most people get them wrong.

[quattro]

Ok thats good advice.... Im not stuck on the dual plenum design i just thought its better, but harder to make then a single....

What kind of size and taper would you suggest on a single plenum maifod then?.....

[quattro]

ps would you be willing to flow mine afet I construct it just to see how good/bad it is?

[Lupo911]

All for making ones own manifold, just don't start with a twin plenumb chamber one. There is an art to getting them right as the first and last cylinder will naturally want to flow more than the middle ones. Whereas a non directional plenumb chamber with big volume comparatively speaking and identical trumpets/stacks/runners to each cylinder is guaranteed to give better results for a novice.

But if you are hell bend on dual design the very general rule is make sure the hole flows the same as the throttle body that way you are not introducing an unnecessary restriction. Likewise everything needs to be radiused to minimise turbulence on the transition between the plenums, as the more turbulance you have the worse th throttle response becomes.

i totally Agree. I would never build an Intake without CAD and CFM Analysys anymore when you see how much difference you get with very small changes, you will be more then surprised.

here is a very good thread of a guy who bulds his own dual chamber intake. He is more than good in whats he is doing...

http://forums.hybridz.org/index.php?showtopic=61549

[quattro]

looks pretty good, that guy knows his *****. Wouldent say the changes he made were minimal they were pretty drastic.....

After reading that ..... im still making one!

[Error404]

those R8 LM intake manifolds are pretty!

The S1 E2 design is like a tripple plenum design with the flow split top and bottom of the intake chamber?

[quattro84]

Indeed, S1 mani has double feeders.

[quattro84]

I had my share of CAD & CFD time trying to improve manifold designs. Did singles and duals, what became obvious to me is that dual designs needs a lot more attention to detail to reach an ultimately even flowing design.
Making a manifold flow for a given air flow isn't that hard, but getting it balanced through out the entire rev range is something else.

So i made a single plenum design and optimised it with supports at less harming places.
A preview of CFD analysis and flowpath distribution:

As shown air density can be quite even, air speed isn't.

This is the best flow distribution i achieved with single plenum design:

That's even less difference than your injectors will give based on normal fuel rail design.

My S1 replica i was working on to get casted at the company (MGG) i worked at that time:


My advise: copy something that does work, and keep it simple (go for single plenum)