01-03 HONDA XR100: FMF Powercore 4 Complete Exhaust With Stainless Hi-Flo Header (Aluminum) FMF developed the PowerCore4 to increase the horsepower and torque throughout the entire power curve producing a noticeable power increase that is useable and compatible with every style of riding. Aluminum construction and stainless steel Hi-Flo endcaps make for the perfect balance of performance and strength. Aluminum performance muffler with durable stainless steel components. Completely redesigned for all late model applications. Removable spark arrestor included on most models (see notes).