In the USA, the WR-450F (and the WR-250F, which I own) roll off the showrooms corked-up with airbox intake restrictions (snorkels), lean carb jetting, and a totally plugged-up exhaust. The bikes are very quiet, but run well below their potential. I can't say exactly how the WR-450F runs off the showroom, but my 2009 WR-250FY was whisper quiet but comical in the throttle response and power output departments. In the USA, the bikes come like this to pass rediculous EPA regulations, and this GYT-R AIS removal kit is sold by Yamaha Motor Corp., USA as an option. It comes with carb jets and needle, a shorter throttle stop to allow full throttle, parts to remove the AIS, and instructions showing how to install these items, as well as perform all of the other "free mods" the USA WRs need to make them run like you'd expect from a 21st century dirt bike.