Zim,
I've got a set on my Rock and they do add a little more power or rather they are do not restrict as much power. I've got a couple of sound clips one with the stock exhaust still on and the other with the Jardines, just so you can compare equally. Here is the Stock pipes
and now the Jars
Heck while I'm at it, has anyone wanted to hear a Rocket with the stock manifold open, no cat box? Here's that one.