i agree and disagree with the opinions in this thread. if you just take off your muff, then yea it could be harmful to your bike. however if its a actual open pipe full exhaust, then i dont forsee a problem. ive had a 4 into 1 open pipe on my bike for years, no problems whatsoever, and ive been in the engine to verify that. ive pulled up next to cops numerous times and if anything they just roll their window up. it will change your a/f mixture so you will have to tune for it. you lose some low end power, gain some high end. whether or not you notice it depends how you ride.