I just removed the baffle from my spare stock muffler and drilled 3 holes in the end cap and put it on just for shits and giggles to see how well it performed. Talk about suprised I had an aluminium muffler called " TK " on the bike when i got it, and i have never heard of it before, its just VERY loud and open an open core design. But now ill be stickin with the modified stock muffler. Ive only been up and down the street so far but im more than impressed. More power, better response and quieter 99 WR400, Whipps alloy bash plate, Acerbis DHH twin lights, One Industries grippa seat cover, YZ timing, grey wire cut, Air box cut and drilled, Renthals, Ego barkbusters, Twin air-air filter, UFO frame guards, gutted stock pipe.