Yep, what he said. They concentrate all the power on the top end where a pipe like Fattys has it all around but not as much. Basically, if you like to have your bike always screaming then the Shearer will work for you. If you like to cruise and hit the trails though it may not be what you are looking for. I'm getting some porting and then I'll do a review of the Shearers v Fatty's. From what I heard it will be night and day.