I have the slip on and I like it alot!!!! I don't know any dyno numbers but the slipon and a rejet with a drop in K&N really picked it up some. Also dynojet recommendations don't work with the pro circuit, They say a 146 main with the clip on 2 for up to 3000 feet I am running a 165 with the clip on 2 and it seems about right. Still in the tuning phase. The pro circuit is very quiet unless you really get in the throttle, I like that part about it.