Originally Posted by stormcrow

single vs. Dual is apples to oranges. Bigger is not always better, even when speaking of fi applications. If it were, why not go 4" or 5"? The reason is that exhaust flows in pulses and if it gets too cool due to a slower rate of flow (bigger exhaust will flow more slowly..especially if oversized for the application) the fluid dynamics change as well as the weight of the air mass. This can cause the exhaust to "back up" in the exhaust sytem and the motor to work harder to expel it.

In truth, with the bends, length, resonators and such in place in different exhausts, it is hard to truly say what diameter exhaust will flow the best. Only flow rate tests can determine this. Who has time for that?

edit - btw, the most restrictive portion of the exhaust system is the manifold(s).