Let's talk intake manifold design

[rs4pro3]

When I was doing research on mine, I found that for the plenum size you want the internal volume to be at least as large or larger then the total engine displacement, My plenum ended up having a volume of 3.2 liters. Runner length all depends where you want peak power, look up Helmholtz frequencies. In my case I ended up using a runner 3 inches shorter then I calculated I needed, but it ended up working perfectly, I may of miss calculated or just got plain lucky :twisted:

[der affe]

^Dimensions on the Dbilas setup would be a great starting point!

Thanks Greg.

what dimensions do you need?
specifically?

[z31maniac]

what dimensions do you need?
specifically?

All of them basically. :D

Runner length/diameter (is there any taper to the runner?), plenum width/height/depth (so I can determine the volume).

Are there velocity stacks inside the plenum?

[Miasma]

http://www.rossmachineracing.com/intakepartspage.html

Lots of parts to make a intake.

I am going to make one for ITB's when I turbo the swap I am planning.

[z31maniac]

Anyone know what the stock throttle body size is?

[Miasma]

M20B25:

Throttle body inlet: 65mm

Throttle body butterfly: 60mm

Throttle body outlet: 63mm


M20B20,23,27:

Throttle body inlet: 55mm

Throttle body butterfly: 48mm

Throttle body outlet: 54mm

[atomic]

I don't have ely's skillz to rig up a homemade ITB setup, nor I'm going to spend $2500+ or whatever it is on the Dbilas setup.

Give these GUYS a call and see what there kit for the M20 is going to cost. Looks like it could be in the $1500 range according to their other kits. They do have listed the triple intakes for the M20 motors in stock...

Here is the new kit for the 24v folks they have developed...

[z31maniac]

If I went ITB's, I'd be tempted to just stick airfilters on the end and not hide their awesomeness under a plenum.

[der affe]

All of them basically. :D

Runner length/diameter (is there any taper to the runner?), plenum width/height/depth (so I can determine the volume).

Are there velocity stacks inside the plenum?

there are no velocity stacks inside the plenum.

I'll check on the runner length, they are all equal length though. i would rather not take off the plenum, because it is literally a 4 hour trial and error deal to get it to seal correctly. if you do ITB's, don't copy this design or make the sleeves longer.

the Dbilas plenum has tapered (OD) runners that make the selves slip around and don't let the hose clamps secure it very well. unfortunately it is a cast unit so they would have to machine flat surfaces onto the OD of the runners and some knurling to hold the sleeves in place.

if you are going to just do a custom plenum with a single throttle body do you want the legnth from the head at the intake flange to the base of the runner where it enters the plenum itself?

[z31maniac]

Yeah, I definitely don't want you to have to take the intake off or anything like that.

If you could just measure the outside dimensions of the plenum, then the length and OD of the runners I think that would be an excellent start.

atomic, I checked out their site, that is some pretty nice looking stuff. You can even buy inserts to "tune" the runner length, very cool indeed. I'm going to shoot them an email today just to see.

Anyone know the runner length/dia of the stock intake?

[atomic]

There was a guy on Bf.c that was trying to get rid of his set because the spacing was just not going to work on his Corrado that he had bought them for. Last I remember he had marked them down to like $900-1000 shipped for 6 brand new 45mm throttle bodies/linkage...

[Miasma]

M20B25:

intake runner length: 360mm

M20B27:

intake runner length: 550mm


Dont know the stock Dia. Sorry.

[TwoJ's]

Do you live close to a university? Know someone with access to a flow bench? Otherwise, I think you will just be shooting in the dark.

And you are doing something I've always wanted to; a high comp naturally aspirated m20. Nice stuff.

[z31maniac]

I don't personally know anyone with a flow bench, but I don't think it would be too tough to find someone in our group that knows someone.

It will still take awhile for it to be complete, I don't want to rush or have to skimp/cheap out on stuff just to get it done sooner. My goal is to have one ready to drop in by the end of the year.

[a_thomasmr23]

there is a ton of info on the web with guys that make there own benches, a project i'll be getting into in better weather.

my understanding to get the equal flow to each cyl. your "airbox" area needs to be 15x the volume of a single cyl which is way to big to fit under a hood i bet. What i was thinking is just make even length to the start of each run to even it out