Originally posted by drift
back pressure is bad.
it's called flow velocity. piping that's too large decreases flow velocity of the exhaust gases.
you have to evacuate the exhaust as fast as possible out the tailpipe to prevent reversion. too large will reduce exhaust gas pressure, unable to maintain flow velocity. too small will become an obstruction, resulting in back pressure.
back pressure and flow velocity are two different things... properly tuned piping will keep exhaust velocities at it's highest speed to evacuate the exhaust and prevent reversion.
You need a certain amount of back pressure or you will lose power.