12-15 YAMAHA WR450F: GYTR FMF Powercore 4 Muffler The PowerCore(r) 4 is designed to increase the horsepower and torque throughout the entire power curve and give you a noticeable power increase that is very usable and beneficial, no matter your riding style or ability. Features include space age internal packing for maximum packing life. High-flow modular end cap. Internal core shape uses high-flow technology. Enhanced sonic evacuation provides for higher flow and increased power.