Well, it will lean out the fuel mixture, which could possibly damage the engine. However, if the bike has a power commander and has been re-mapped for proper air/fuel ratio, then that pipe won't hurt anything. I would suggest you get it to a dyno and take a look at the A/F ratio throughout the power curve. If it's too lean, you have two choices: spend the money on a power commander and a custom map, or spend the money on a new pipe. Personally, if the pipe sounds good, I'd just get the power commander and custom map. Heck, even a normal slip-on will lean out the A/F ratio a bit and you'd be smart to have a power commander there as well.