ORIGINAL: ICEMAN_CH

I know this is going to create an argument but here it goes. Backpressure is a bad thing that is commonly misunderstood. It used to be thought that backpressue would help to close the exhaust valve quicker giving you more time to fill the cylinder with air and gas giving you more perfomance. If this was the case why aren't we all running 1" pipes. The truth is you want the exhaust gas to have a constant velocity. This way exhaust gas can move freely and smoothly out of the system. If you throw a 6" pipe on for your exhaust then when the gas leaves the cylinder it's going to expand causing it to slow way downand rob you of performance. So you need to strike a balance. Something small enough that the gas dosen't slow down and something big enough that it can still move freely. If you get this balance correct then the momentum of the gas will actually create a negative pressure behind it (It sucks). This will create a negative pressure in the cylinder helping the exhaust valve close and increseing the amount of air into the cylinder.