I went from a dual 2 1/4" with stock manifold and rear can only to a Stahl header with 3" pipe plus high flow resonator and muffler. Gained a lot, I did feel a slight loss of torque but the net result was far better. As well, I put $$ into the head with a cam. More air is coming in and now more is allowed to go out. But it would seem to me that one ony needs to look at dragsters for the answer on exhausts. Back pressure, not! But the intake and fuel system is designed for it. Just like suspensions, can't do springs without doing shocks, etc. Better the exhaust system, means you gotta better the intake for the proper results. My 635 cents worth....