just got the sickbike parts expansion chamber exhaust and it adds crazy power, i had it on my singlespeed beach cruiser with a 32t sprokcet and hit 39.5 mph on a slightly inclined street vs 35.9 originally. i just put it on my 7 speed mtn bike with a shift kit and im popping wheelies in first gear and have yet to record my top speed, but this thing is awesome.