The O. S. 55HZ-H Hyper Ringed Heli engine is cause to rejoice for 3D heli fliers! The 55-HZ-H Hyper Ringed engine cranks out optimum power with a minimum of space! The PowerBoost Pipe 50/55 is a first from O.S. – designed especially for helis, improving efficiency and power while featuring a compact size. It also fits the 50SX-H Hyper Ringed heli engine. * Features the same mounting pattern and silencer size as the 50SX-H Hyper engine. * Dual needle 40L carburetor with four-arm throttle lever is designed to optimize the power, performance and reliability of the 55HZ. * Produces a range of 2,000 - 20,000 rpm. SPECIFICATIONS Displacement: 0.55 cu in (8.93 cc) Bore: 0.91 in (23 mm) Stroke: 0.85 in (21.5 mm) Practical rpm: 2,000-20,000 Weight: 14.39 oz (408 g) Power Output: 2.1 hp @ 17,000 rpm Weight: 14.39 oz (408 g)