Features: The straight through design of the spark arrestor canister and the performance flow stainless steel end cap ensures strength, durability and most importantly, track and trail proven unrestricted power. The 2.1 utilizes a shape inspired by the 4.1 system. Utilizes exclusive FMF "Turbine Dampening System". U.S. Forest Service legal status. NOTE: Will not pass 2025 FIM sound regulation.