Muffler

Engine masters did a show on quieting a thousand horsepower, all using the big ovals, rather than the bullets. 4 inch in and out. The hooker maxflow won the test, best power, cheapest, and second on quiet. Quietest was a Flowmaster 30, and it didn't cost over ten horsepower on a 1000hp motor, compared to the straight-thru's.
Edit: others in the test were borla and magnaflow.