I am ordering a muffler today. I will also change the piping from the cat to the muffler. I am not getting a whole preassembled exhaust system but just having the pipe size change. BUT I have no idea what size to change it to(for hp, torque, gas milage etc.). I am afraid if i change to the wrong size I might lose power at some revs. What should I go with, I believe mine is 2 1/4" right now. Regardless, what size should I change it to, has anyone done it before to their 5th generation AV6? And lets say I decide not to change it, if my original size is 2 1/4", and the inlet for the new muffler is 2 1/2", if they do a conversion to fit them together, will it affect anything(sound, power, gas)? Thanks