Originally Posted by xntrik
Said all that to say.... ram effect, too short or too long...... depends on scavenging
Sort of. Actually, pressure/vacuum waves exist in both intake and exhaust runners. Both can be tuned independently. Design the intake to have a pressure maximum at intake valve closing and the exhaust to have a pressure minimum ('scavenging') at exhaust valve closing. My senior project @ Fresno State was designing and building independently tuned intake and exhaust manifolds for a 1 lung Briggs and Stratton 5hp engine. I designed and built a port pressure recorder that tracked pressure for the entire cycle of the engine at a given port and I calibrated the manifold designs using that and a dyno. Got a really good power boost at design rpm but of course gave up power at other rpms. I compared stock manifolds to the tuned ones and the stock ones had no big high or low pressures. No big power boost but no power loss at off optimal pressure points, thus a nice flat torque curve. Tunnels were invented to do just that on a V8 - max HP at optimal rpm, giving up power at other rpms. By design they have a peaky torque curve. They can be made to run on the street but they were designed for WOT at the drags. That's a fact.