This is the O.S. .91HZ F3C Competition Helicopter Engine.

FEATURES: 
* Designed specifically for F3C aerobatic competition
* Rectangular heat sink allows engine to be enclosed entirely inside cooling shroud
* 61-B carburetor with thermal insulator to block heat and a needle valve control lever to control mixture from transmitter
* Newly designed piston and crankshaft for reduced vibration and improved torque stability over entire RPM range
* Ball bearing supported crankshaft
* One year limited warranty

INCLUDES:
* (1) O.S. .91 HZ F3C Competition Helicopter Engine with #8 glow plug, needle control lever, 
extra 0.2mm head gasket, cap screws and instruction manual.

REQUIRES: 
* Fuel: 10%-30% nitromethane with at least 18% lubricant. Lubricants may be either castor or synthetic oil or castor/synthetic blend.
* Field Equipment: glow starter, fuel bulb, fuel can filter, fuel pump hexagonal starting shaft 
(depending on brand of helicopter) electric starter, battery and fuel tubing
* Muffler - This is specific to the heli

SPECS:  
* Displacement: 0.91 cu in (14.95 cc)
* Bore: 1.09" (27.7mm)
* Stroke: 0.98" (24.8mm)
* Output: 3.4 hp @ 15,000 RPM
* Practical RPM Range: 2000-16,000
* Weight Without Muffler: 1.36lb (618g)
* Height from crankcase bottom to top of cylinder head: 3.9" (99mm)
* Height/bottom of mounting tab to top of cylinder head: 3.2" (81.2mm)
* Distance between mounting holes same side: 0.98" (25mm)
* Distance between mounting holes opposite side: 2.04" (52mm)
* Distance between muffler screw holes: 1.6" (42mm)
* Distance/bottom of mounting tab to muffler screw holes: 1.7" (42.8mm)
* Length from front bearing to back plate: 3.3" (84mm)
* Length from back plate to end of crankshaft: 4.9" (125.6mm)
* Width of crankcase below mounting tabs: 1.7" (43mm)