This is the Pro .50H Ringed Two Stroke Helicopter Engine from Thunder Tiger.

FEATURES: Fits all popular 46-50 size helicopters with gear ratios between
            8.5:1 to 9.1:1
          Developes peak horsepower at 14,000-17,000RPM
          Crankshaft supported by two ball bearings
          Lightened hypereutectic machined Al-Si ringed piston
          Two-needle air-bleed carburetor
          XC2 (extreme composite) cylinder liner coating with a criss-cross
            pattern etched on the sleeve wall
          Rear reinforced resin cage ball bearing support
          Three year limited warranty through Hobby Services beginning at date
            of purchase

INCLUDES: Pro .50H Helicopter Engine with 1.5, 2.5mm hex wrenches, decal
            sheet and instruction manual

REQUIRES: Fuel: Heli blend with 5-30% nitromethane and 20% lubricant content
          Glow Plug: Long type such as the OS #8
          Glow starter, plug wrench and field equipment

SPECS:    Displacement .50cu in (8.19cc)
          Bore: 0.886" (22.5mm)
          Stroke: 0.811" (20.6mm / 0.811 in.
          Practical RPM: 2,000 - 17,000RPM
          Output: 1.8 BHP/16,000 RPM
          Weight: 14.28oz (405g)
          Crankshaft Size: 1/4-28

            Carburetor Settings*;
          Needle Valve: Three turns from closed position
          Mixture Metering Screw: 15-30° degrees clockwise
            *Carburetor was preset at factory and requires only small
             adjustments
          Distance/top of cylinder head-bottom of mounting tabs: 2.72" (69.1mm)
          Distance/top of cylinder head-bottom of crankcase: 3.4" (86.4mm)
          Distance between mounting holes same side: 0.67" (17mm)
          Distance between mounting holes opposite side: 1.7" (43.2mm)
          Cylinder head width: 1.8" (45.4mm)
          Width at mounting tabs: 1.96 (50mm)
          Width of crankcase below mounting tabs: 1.34" (34mm)
          Center of engine to front bearing: 2.37" (60.3mm)
          Backplate to front bearing: 3.34" (84.9mm)

                                                                   jxs 10/18/10
                                                                         ir/jxs