[ERP]

This is my understanding of the whole back pressure situation. It could be drivell, but the guy who relayed seemed to know what he was talking about.

The pulse of exhaust gas caused by a previous cylinder firing can actually helps a cylinder expell the exhaust gas, the more restrictive exhaust basically increases this effect, and at low RPM it can result in more torque. In extreme cases reducing back pressure can reduce torque accross the entire rev range.

However with more aggressive cam profiles, the effect is reduced and the backpressure can restrict the engine accross the entire rev range.

A case in point is the post 2000 Viper engines, my understanding is that they are less friendly to exhausts with reduced back pressure (than the pre 2000 engines) largely due to a less aggressive cam profile.

As I said could be drivell but it sounded like a reasonable explanation when it was relayed to me.