Question about header outlet size and system diameter

[sickpuppy1]

Garm is right about a little back pressure is a good thing. Exhaust goes out in small pulses as each cylinder fires. With a properly sized exhaust you will get a light "scavenging effect". In other words, one pulses moving out the exhaust tends to pull out exhaust as another pulses is moving out so it pulls and pushes it way out, in harmony so to speak, hence the name "tuned" exhaust. With a system that's over sized it will actually stop in the pipe, so it has to push only on its way out...no scavenging effect so the cylinder is no totally purged,hence less power. A system that's too small has to literally push it out and has to use power just to get rid of exhaust!!
On V8's, many higher end full exhaust systems will put a crossover pipe in between the two side to help increase the scavenging effect. This is only one of the reasons why the higher cost of a name brand systems cost more...They actually domputer design and then dyno the headers to know what length pipe,diameter will do best and collector legnth etc. So copycat systems will emulate what megan or whom ever have designed. Are there differences? Yes! Materials used, weld type and quality etc add up. Now is there enough of a difference for joe daily driver to notice? probably not. Garms car will, thats for sure, but he's a cutting edge kinda guy with more HP than 99.8% of us will ever get to. Lucky stiff......