924Board.org

[OutOfTheBox]

I want to design an inlet manifold from scratch using ACAD.

I want to put the plenum down at the bottom of the engine, because thats where my intercooler is, which saves me almost a meter in piping.

Also thats where the cool air is, so my plenum will be in the air running underneath the car(diverted up by the tray at the bottom of the engine ).

Anyone got any suggestions about header length, plenum volume, diffuser shape type etc.

I want to use a cone for the plenum, because I believe the optimal shape to use, is the same as you see on an intercooler. They don't use a square can at each end.

I got the actual calculations somewhere for the shape to use, I used this for a solar collector. The sun shines on a "radiator" and you pump water through it, which turns to steam, which drives a turbine.

As nearly all the plenums I've seen are tube shaped it must be because max flow is achieved with a cone plenum, but the best balance of flow is with a tube plenum ?

Anyone know why ?

I need to finish this project within 8 weeks, any help would be much appreciated.

[Rasta Monsta]

My 2 cents:

The tube shaped plenum may be easiest to design/manufacture, or it may be the most efficient. . .the most important thing, IMO, is that the runners have as much volume as you can get out of them.
_________________
Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[endwrench]

The way I understand it, the use of a tube plenum is for volume. This allows the air a chance to redirect itself to the runners and allowing for better, more even distribution.

Not real sure what you mean by a cone plenum. Are you talking a center inlet to a flat "funnel" connected to the runners? I always thought this would work well if you have the room. It is still just a large plenum with better directional flow than an end inlet tube plenum or even a center inlet tube plenum.

Maybe you could show an xample of a cone plenum.

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[OutOfTheBox]

[Rasta Monsta]

[OutOfTheBox]

[Min]

and it also lived its life at wide open throttle. Drivability is a concern in your case I think. Having the throttle there would 'work'.

Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.

[-nick]

The GTR had the TB before the IC too I believe. I always wondered about that, but I suppose at 80-100% throttle it doesn't matter much.

Whatever you do, use venturi's at the end of your runners inside the plenum. Makes a significant difference in flow. The one thing I regret not adding to mine.
_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

[Peter_in_AU]

As for length of the runners, unless you want to change your power-band just measure the factory runners.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

[Min]

http://www.velocity-of-sound.com/

has a induction wave caclulator, and of course sells some very nice looking velocity stacks.

If I didn't make my own velocity stacks I'd have purchased them from there.

Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.