I went from the stock exhaust on my 06 to a 4.5 inch / 5 inch combo straight pipe (no cat or muf [wow that sounds like a bad porno ]). You can check my Dyno Run for the sound of that set up. Had plenty of turbo sounds from that. The hubby was not so happy with the sound in the cab though. So he put a 5 inch Diamond Eye kit w/ a muffler on it. It is still plenty loud! (IMHO I actually think there is more drone now though...but shhh don't tell him)