Originally Posted by Bosch_Dealer
The size of the runners should be the same size as the intake port mate
The length of the runners is dictated largely by the RPM range you want them to be most effective at.
Originally Posted by Bosch_Dealer
and the volume should be around 100% of what your cylinder displaces
..the actual plenum size is the same as the total engine displacement..
Optimum plenum volume is almost never the same as engine volume.
Corky Bell recomends around 50-70% of displacement.
Its quite obvious why it doesnt need to be as much as the engine volume really when you think that on a 4 cylinder engine, only 1/4 of the volume at a time is required from the plenum during an induction stroke.
Can you tell us a bit more about the engine you have, what you are using it for etc?
Ultimately though, its going to be trial and error to get the perfect volume.
Reality is, even if you get it very wrong, it dont drive *much* different, plenum volume is far less important than a lot of people give it credit for (thats not to say it doesnt matter, but its certainly not going to make huge differences that ruin the car if you get it a bit wrong)