hello,

i have searched this site in regards to intake manifold design, i found one kinda useful post that ended up with good information, but didn't quite give me all the answers. this will be my first intake manifold i've made so figure it wont be perfect first time,

i have read and come to the conclusion (from what 90% of people say) that the plenum volumn needs to be around 1.5-2 times the size of the engine capacity, 1600cc, so around 3.2L.

i've also been researching runner lengths, and most aftermarket manifolds seem to be made with alot shorter runners than their standard NA equivalent. so i was thinking around 4-5inchs long. would this help move the torque up higher? i will be using 2inch 3mm wall tube, as i will form the end to match the port size.

now the thing i want some advice on is bellmouths, originally i was going to use a 10mm alloy plate and machine a bellmouth into it. would this be ok, or is it more beneficial to use proper bellmouths that extend above the base of the plenum like most NA guys do?

here is a pic of my standard manifold. it also has tvis in there, (one butterfly on each pair of runners) i will be getting rid of this.




any other thoughts are welcome.
thanks


Modified by ae924agte at 11:09 PM 3/14/2008

 

from all of my personal experience with it...

make the plenum as large as possible...given the space requirements. The only thing this will sacrifice is throttle response. So if TR is really important to you... size the plenum accordingly.

Runner length... shorter runners shift the torque curve up the rpm band. resonance/helmholtz tuning..yada yada. On the dyno...thats what it does....literally. With a turbocharger in the mix... you wont have much vacuum in the manifold lol.... but still you'll have what i like to call a "relative" vacuum. compared to everywhere else...there is less pressure. Don't pull your hair out on this one.

Bellmouths. Should be off the port floor. Should be a 180deg stack. Should NOT be a constant radius, but an elliptical shape.

Thing I'd like to add.... no large changes in cross sectional area as the air enters from the TB to the plenum....this creates a large pressure drop across the port and KILLS the airspeed.

Remember Air has mass...and therefor has inertia. try to keep the air flow to all cylinders the same so you dont have a large cylinder variance (less than 3% is excellent IMO)