I rode with the mufflers off for about 1000 miles. I noticed the popping on deceleration but the bike ran pretty good other than that. The dealership told me it wasn't recommended and to keep an eye on the operating temp. There definitely was some sort of shift in power like HeMan said. I now have the Termignoni shorty and the bike is running really good. There's nothing to the shorty and I have heard of people using it on the S2R. It's basically just a two into one with a carbon sleeve and a hefty price tag.