Brand New! FMF Factory 4.1 RCT Slip-On Muffler - 2018-2024 Yamaha YZ450F The Factory 4.1 RCT incorporates FMF's Resonance Chamber Technology™ both internally and externally In addition, FMF achieves a shorter overall length that is less susceptible to crash damage and complementary to their Factory Forward Engineering - moving the muffler closer to the motor to centralize mass The Factory 4.1 RCT is constructed from only aerospace grade materials that meet their exacting specifications and is manufactured 100% at their Southern California factory Massive Power gains throughout the RPM range. Huge weight savings RTS (Rapid Tuning System)