I have the Kerker Stouts on my CVO now. Mean sounding pipe. Very low growl to them. As of now I still have the cat in. That being said, I really dont know if there is a power gain. I did find this out. If you install these even if you dont change your head pipe, you will need to have your bike tuned. Mine is running a little too lean now and I'm getting a little decell pop and once in a while will backfire and stall while idling in gear. maybe after a tune you will see a gain in power.