Question on Intake Manifold Plenum Design

[colnago]

No, this isn't anything like my "bad intake" question. This is just out of curiosity.

I've noticed that many of the dual-plane designs have a bumpy or wavy bottom, but open plenums tend to be smooth on the bottom. I was just wondering why. Any ideas? Does it create turbulence for dual-plane, but it needs a smoother flow in a single-plane design?

Joseph

[Ranchero50]

Due to energy pulses in the air stream caused by the intake valve closing, a longer intake path changes the resonance frequency to a lower pitch which increases the low end torque. There's a ton of engineering involved but you see it in industry on EFI intakes with really long runners and intake gate valves that select between long or short runners on some of the 4.6 liter's. With the advent of variable cam timing the engineers were able to get away from the dual runner intakes and still have similar (or better) results.

Download a free copy of the two stroke tuners handbook and read the sections on exhaust design. Fascinating stuff.