POWERCORE 4: When designing the PowerCore 4, FMF looked at their top of the line products to deliver race-inspired performance at an economical price. The end result is a quality 4 stroke muffler with improved torque, increased horsepower and rugged durability all at a price that wont break the bank. Massive power gains throughout the RPM range Huge weight savings Rapid Tuning System (RTS) FMF uses the highest quality proprietary blend of alloy grade titanium made specifially to their standards Can be used with FMF or stock OEM header pipes We recommend all motorcycle parts are fitted and tested by qualified professionals. Fits: Yamaha WR450F 2003-2006 YZ250F 2003-2005 YZ450F 2003-2005