Originally Posted by snrusnak
Without starting a pissing match, the back pressure thing is incorrect, although just about everybody and their mother believes it. Back pressure is always bad(yes, even for low end torque). The reason you'd lose low end torque with a full 3" dual setup is because you'd slow exhaust gas velocity tremendously with the larger diameter pipe. There's a balance to find the proper pipe diameter to achieve the most volumetric flow at the highest velocity. With too big a diameter you reduce velocity, but with too small a diameter you choke the engine. Back pressure has nothing to do with scavenging. Higher velocity will yield more scavenging effect.
You're gonna' start a pissing match, Sean.