YS Series YS 50ST Heli Type 2-Stroke, Helicopter Displacement .499 cu in (8.17cc) Bore .866" (22mm) Stroke .847" (21.5mm) RPM Range 2,000-20,000 Output (HP/rpm) - Weight (engine only) 14.13 oz. (400g) Crankshaft Thread - Propeller Range - Included Decal Sheet, Instructions