I just put a super 40 on my TJ, and I can say its louder than I thought, it has a nice deep tone but its a little loud when you give it some throttle. I haven't ridden at highway speeds yet but I'm going to guess there is a slight "drone" sound hen you settle into a speed. Overall though a nice product. For a stock TJ you need 2.25 in Piping, Center Inlet, offset outlet.
Here's a pic of mine going in: