OS SPEED R21 GT is an all-new 5-port engine. It features a newly developed piston and 5-port cylinder, crankshaft, crankcase, Specially made to fit on-road GT track. The OS SPEED R21 GT has a 7mm carburetor restrictor. Tech specifications: Displacement: 3.49 cc Bore: 16.08mm Stroke: 17.20mm Intake ports: 5-port Exhaust port: 3-port Practical RPM range: 4,000 – 42,000 rpm Max. power output: 2.65 ps / 2.61 hp / 34,000 rpm Weight: 369Gr.