I'm trying to remember .... I'll get close. Removing the cats gets most of the gains, leave them and any changes are for sound quality and not performance. The difference on my car was 16 hp from removing the 4 cats. Open downpipes (Needswings) moved the total to 26 hp. Open headers was another 7 hp. Headers with stock resonator back was 4 hp. So the resonator and muffler only cost you 3 hp. These are peak numbers. Some changes lost some low end torque. If I had to do it over again I'd go another route with my disposable income. I may, in the future, remove the resonator and muffler and put something light weight, but not for power gains. For weight savings only.

Les