See: FX Royal Racing Engines

FX Engines have introduced the new K501 3.5cc nitro engine. Based on the innovative K5, the 5-port engine features a DLC-coated and tungsten balanced crankshaft, specially selected and matched sleeve and piston set, ceramic bearings as well as a 10 ribs cooling head. The K501 is designed to provide maximum power at bottom and middle-range.