FMF Racing Powercore 4 Aluminum Slip-On Muffler w/Stainless End Cap for Yamaha YZ250F/YZ450F 06-09/WR250F 07-14/450F 07-11FMF PowerCore 4 Slip On Exhaust Yamaha YZ250F YZ450F WR250F WR450F When designing the PowerCore 4 Exhaust, FMF took a hard look at their top of the line mufflers to produce race inspired performance at a more economical price. The end result is a quality muffler that delivers improved torque, increased horsepower and rugged durability all at a price that won't break the bank. Features: Increase in power and torque through entire RPM range Durable