Sport aviation engines for Ultralights, Homebuilts, Kitplanes, Gyrocopters, Helicopters, Powered Parachutes, Trykes, Hovercraft & Air Boats.

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3702 - 3 cylinder - 2 cycle liquid cooled 84hp

The 3702 is Hirth's water-cooled alternative to the popular 3003 air cooled engine. 3702 is offered carbureted or with optional fuel injection. Standard engine is pre-mix and oil injection is available for either the carb or fuel injected versions. A narrow engine profile with a single tuned exhaust used for all 3 cylinders allows the 3702 to be used in compact engine compartments. Pistons fire 120 degrees apart resulting in a very smooth power curve. 3702 fuel consumption rivals similar Hp 4 cycle engines.

3702 incorporates Al-Nikasil coated cylinders for superior performance and reliability. Nikasil provides for a super low coefficient of friction, reducing engine heat and wear. The pistons and cylinders expand at the same rate thus providing for a seizure resistant engine. 3702 crankshaft is 4130 chrome molly steel. Heads, cylinders, rings, block casting, connecting rods and associated components are all of the highest grade alloys available today.

Alternate Views:

3702 - 84Hp electric start &
3 carburetors.
3702 - 84Hp elec,st, carbs & G-50 gearbox
3702 - 84Hp electric start &
Electronic fuel injection.
3702 84Hp with electric start fuel injection & G-50 gearbox
Oil Injection Option

Hirth's latest design.

Engine Type:
2 cycle, 3 cylinder
HP Output:
84Hp @ 4950Rpm
Peak Torque
87 Ft.Lbs @ 4300Rpm
Dual CDI
(Capacitive digital Ign.)
Triple 34mm slide or optional electronic fuel injection
Fuel Pump:
Auxiliary external pneumatic - 12VDC with fuel injection
Premix – 50:1 or optional oil injection
Counter clockwise, viewed from output end
12 volt electric,
250 watt/20 amp alternator standard
Liquid cooled
108 lbs- including electric start and exhaust. With optional gearbox 127 lbs. (does not include radiator)
Reduction Units:
G-50 gearbox available in - 2.16:1, 2.29:1, 2.59:1 ratios or optional G-40 gearbox can be used if clutch is required.
Drive Coupling:
Elastomeric dampener with G-50 gearbox or optional centrifugal clutch with G-40 gearbox. (2.03:1, 2,25:1, 2.64:1, 2.96:1. 3.33:1)

3702 is the high torque low RPM version of the 3703 engine. This is done through engineering by changing the piston port timing. Placement of the port timing determines what Rpm the peak torque is achieved. When peak torque is arrived at low Rpms the peak Hp of the engine is less but the torque curve in mid range is very flat. Such an engine gives up some thrust at full power but has high torque in the mid range allowing for very low engine RPM at cruise power settings.

3702 High torque/low rpm engine - Peak power - 84 Hp at 4950 RPM.

Engine Print

Customer Photo Gallery

3702 installed on MX II
Picture #1 Left Side
Right Side

3702 installed on Earthstar Thundergull II
Picture #1 Left Side
Right Side

3702 installed on Dolphin Floatplane
Picture #1 Left Side
Right Side

3702 installed on Skymaster PPC
Picture #1 Left Side
Right Side Rear View

3702 installed on Gyrocopter
Picture #1 Left Side
Right Side

3702 installed on Infinity PPC
Picture #1 Left Side
Right Side

3702 installed on Fusion PPC
Picture #1 Right Side

3702 installed on Skyboy
Picture #1 Left Side
Right Side

3702 on Genesis Aircraft
Picture #1 Picture #2
Picture #3 Picture #4