You can run a slip-on exhaust without a Power Commander, your bike may idle a little rough,but you can run it. If you were to go to a full system,then you would defenitly need a PC to straighten out the air/fuel mixture. You'll also notice a weight difference between the stock can and an aftermarket( the stock can has a catalytic converter inside),which translates into better handling,exelerating and braking. As I said earlier,I run a slip-on with a K&N filter and a PC with a custom map and I got an extra 7 horses over stock. But be warned,do some research into the different slip-on available,their not all made the same. I had a Leo-Vince before my FMF and my bike ran like crap but with the FMF even before I got the map, my bike ran really good,and sounded better. Hope this helps. :thumbup