04-09 YAMAHA YFZ450: HMF Competition Complete Exhaust - Elliptical (Black) Arguably the highest performing after-market exhaust on the market, the HMF Competition Series is a pure blend between optimized performance and versatility. The secret to it's power lies within the Trimax Core. This unique triangular core accepts specially designed exhaust inserts that provide the rider the ability to quickly change the power and sound according to the current riding conditions Designed and tested for dirt bikes and ATVs. The Competition Series distributes power evenly throughout the entire RPM range. The Competition Series uses a mechanical core to control exhaust pulses and set power levels where they're needed.