all depends on what part of the rev range you use and want to maximise. For midrange torque though, yes you need the backpressure, but if you are looking at running at peek revs all the time, like on the track then the less restriction the better. But even then you need the exhaust tuned to the right frequency range (ie the correct length and diameter) to maximise the harmonics of the entire system at the rev range you most wish to use. i was refering to street use, not track hehe.