The Pro Circuit YZ125 pipe positively affects the dirt bike. The combination of the R-305 muffler and the Works Pipe increases the power from the bottom-end to the very top. Before I was even on the track I knew this pipe was an improvement just because it looks cool. The stock YZ has lots of low-end power but the Pro Circuit system gives it even more torque. The pipe really increased the top-end power by giving it more meat up there and allows it to pull longer. The only downside to this pipe is you will need to scrub the pipe with a rust repellent to keep it shining.