FMF Factory 4.1 Muffler KX250F/X 2021-2024 042396 1821-2036RCT (Resonance Chamber Technology) features a patented core shape that lowers decibels while maintaining maximum power output Internal ducts in the chambers of the RCT system increase internal volume for improved exhaust flow, resulting in power gains throughout the entire range of power FMF's Factory Forward Engineering centralizes mass and is less prone to crash damage Innovative rear end cap features simple installation of tuning tip inserts or