This is the O.S. Max .91 RZ-H Rear Exhaust Helicopter Engine. FEATURES: Aluminum cylinder head, anodized blue in color Designed for Hirobo and other scale helicopters where engine must fit inside canopy to preserve heli"s scale lines Ringed piston 60M-C 3-needle carburetor with mid-range needle for precise adjustments Two year warranty INCLUDES: O.S. Max .91 RZ-H Rear Exhaust Helicopter Engine with #8 glow plug, instruction manual REQUIRES: Fuel: Heli blend with 10-30% nitro content SPECS: Needle Settings; High Speed Needle Valve: Two turns OPEN from fully closed Idle Mixture Control Screw: Factory setting Medium Speed Needle Valve: Two turns OPEN from fully closed Displacement: 0.912 cid (14.95 cc) Bore: 1.091" (27.7mm) Stroke: 0.976" (24.8mm) Practical RPM: 2000-16,000 Power Output: 3.3 PS, 3.25 HP @ 15,000 RPM Weight: 21.8oz (618g) Crankshaft Size: 5/16-24 Distance Between Mounting Holes Same Side: 0.98" (25mm) Distance Between Mounting Holes Opposite Side: 2" (52mm) Distance From Back Plate to Front Bearing: 3.3" (83.8mm) Distance From Back Plate to Crancase Center: 1.1" (27.4mm) Distance From Crankcase Center to Front Bearing: 2.2" (56.4mm) Distance From Crankcase Center to End of Crankshaft: 3.5" (88.7mm) Width at Mounting Tabs: 2.4" (61mm) Width of Crankcase Below Mounting Tabs: 1.7" (42.6mm) Distance from Throttle Lever to Center of Crankcase: 1.7" (42.5mm) Distance/Bottom of Mounting Tab/Top of Cylinder Head: 3.4" (87.4mm)