sensi09

I believe those extra canisters on the HKS are for sound reduction and avoidance of drone.

"Backpressure tubes"? Forget what you've heard, but backpressure is a bad thing and kills power. Initialgemini had it right, as exhaust velocity is key. The key is to match pipe diameter to give the greatest exhaust velocity with the least amount of backpressure and of course matching to your power band. A narrow pipe will have greater velocity at low RPMs while a wider pipe will flow better at high RPMs so a well-designed exhaust will take this into account and should have a correct balance.