I have heard this back pressure myth alot from my quad/dirt bike buddies since i was a kid. Mostly they say it because, "no back pressure burns out your valves." Which isn't true. Its just the air flows better, which needs more fuel. I am not a car expert, and the idea of more "back pressure" equalling more torque sounds believable, and i have read and seen dyno charts that say the same thing on the raptor forum i am on. Duner guys want wot power and have large diameter exhausts, and trail riders/woods racers go with a smaller diameter to keep more torque. But again i only know 1 cylinder, not 4 or more.
Sportlines and fe5-17x7 prime 142 wheels-225/45 achilles atr sports-slotted rotors-nightshaded tails with bowtie for legal purposes :( -shorty antenna-cavi short shifter-spectre intake piping with k&n drop in and the airbox mod+a little extra i thought up-thrush12"turbo muffler with 2-1/4" catback piping-pioneer avh1500 dvd headunit-pioneer 3 way 6.5 fronts-pioneer 3 way 6x9's rear-pioneer gtx5500 amp-12"kicker cvr (soon to be 2 pioneer 10's in custom boxes and another gtx5500.