Paulyy

I was actually going to just write out the formula from my book, but then found a reference to this website. I would love to build my own intake, if i only knew my cam specs i could follow the formula.

Voith

This kind of plenum is used more or less on all WRC cars and was also used on Audi S1 and other cars from Grupe B.. All turbos.

I will design one that will be something between these two. Too bad our brake booster is taking up so much space.

333pg333

While those intakes are on turbo cars they're on small capacity rally motors which need quick low down acceleration rather than more power up top on a race motor.

Removing your brake booster is an easy decision. Change to a pedal box and be done with it.

grumpyf14d

After doing some lengthy research, I thought Audi's concept was best and spoke volumes considering the success of the car and engine. Now understanding what the total volume of the plenum needs to be is as important as the shape.

333pg333

Well volume is another thing that seems to get a lot of different opinions or beliefs. We don't seem to count the pipe from t/body as part of the plenum volume either.

Guess the bottom line is that unless we make and compare intakes we are doing a fair bit of guess work and with tune-able ECUs and knock systems we can work around seemingly pretty agricultural setups (as seen on mostly other modified turbo cars).

Raceboy

I did the dual-plenum intakes both on my 931 2litre engine and my 2.5 16v. Inside the main plenum are 70mm velocity stacks:

Voith

I envy your awesome skills raceboy

mikey_audiogeek

Hi Patrick,
The split/tapered plenum is designed to give even flow distribution to all cylinders under all conditions. In my opinion much more important than bellmouthing the runners. Best off-the-shelf manifolds I've seen are the Jenvey ones from the UK. The calculations for the slot dimensions and manifold taper rate should take into account the velocity pressure of the air, something that isn't replicated on the flowbench.
We took a different tack with our motor - dual throttles, one at each end of the manifold. Reduced the issue by 75%, but created some others...
Cheers,
Mike

mikey_audiogeek

Nope, definitely more suitable for turbos. Bigger payoff.
Cheers,
Mike

Raceboy

I personally would not make any intake manifold without velocity stacks...

Dutch944

I've used the velocity stacks in my intake as well, i can measure the outside diameter for you Patrick, but i think i'm close to 100mm as well, as we had to make a small dent in the stacks to make them fit.

My intake is actually completely build up like your drawing, except for the fact that is not really getting any smaller on the other side of where the velocity stacks are.

Do you want to measure mine completely? Ofcourse it's for 16v but in big lines it should be similar for 8v!

333pg333

Yes, I was more surmising on the turbo or n/a thing there Mike. It's still possible that they're more suited to lower rpm response and clearly the main idea is to have even distribution of flow.

Thanks for re posting that Jenvey name. I had looked at these in the past and now wonder how well they'd be suited to our particular motor and of course packaging. Looks like you could run one of their intakes and some velocity stacks. The added attraction of this intake is the cast nature assuming it would resist collapsing. The other aspect we need to consider is location and size of turbo and wanting to keep the intake away from there as much as possible.


http://www.jenvey.co.uk/home/turbo-p...g-70mm-aplc-70

333pg333

Thanks Bas. Do you have the specs on your stacks? Do you have a pic/s of the stacks sitting inside the plenum before it's sealed up? The reason that I am considering the 'side taper' is only due to size of turbo and heat etc. Seems like you've clearanced yours while retaining a thick plenum all the way across. btw, how thick is your plenum from top to bottom ?

gruhsy

I would think if enough people were interested Michael Mount might make 2V ITB's

Raceboy

There are NO issues absolutely with collapsing at all with custom intakes. There may be if the plenums are made of 1mm sheet aluminium, but not when built with common sens of engineering in mind.

We have ran our custom built intakes up to 3 bars of boost (=4 bars of absolute pressure) and no issues whatsoever.

I would suggest not to overthink the ideas, just use your common sense, some math and then some skills and you will get the best result.