Gernby

Without actually doing some testing, it's very hard to predict how mixed components will interact with each other. If you think of the intake, engine, and exhaust as a 2 dimentional water-way, and think about how water waves will bounce around and interact with the timed openings of a central chamber ... you'll understand how hard it would be to determine whether an increase or decrease in the width of a passage might increae or decrease the water level within the central chamber as the "doors" closed.

The only generality I can state with confidence is that increases in pipe diameter will always create a vacuum pulse (scavenging) back to the engine and decreases in diameter will always create a positive pressure pulse (plugging) back to the engine. Depending on where those diameter changes occur, they will increase or decrease torque at a particular RPM. These pulses have MUCH more impact on a VTEC motor, due to the overlap in valve timing. Basically, those pressure waves are able to pass right through the chamber from the exhaust into the intake ...

From what I have seen, I believe the whole concept of "velocity" is bogus for NA applications. I don't believe increased velocity of the exhaust gas is EVER good for anything other than turbos. However, when you maintain the potential energy of the exhaust pulse by keeping the pipe diameter small for a certain length, then convert that potential enerty into a scavening pulse (rarefraction wave) back to the motor, the benefits can outweigh the cost of the high exhaust gas velocity (restriction).