We have to run full exhaust in our KOS series here, so we have played around a lot with our exhaust. Not to say we know everything, but in my experience the exhaust system is way more of a power robber than the headers themselves.

We have tried a lot of different exhaust combos on the Cuda and in the end I just put electric cut-outs on it. That way it is quiet enough to keep the cops off my butt while in town.

3 1/2" or 4" exhaust was just so large, cumbersome and expensive, that it was just not practical. Besides, no matter what I tried, it robbed HP. And a lot more than 8 HP.

I run 3 1/2" to the dumps and then 3" on out the back. Much easier, cleaner, cheaper and no clearance issues. Besides, I can make it as loud as I want any time I want.