O-150/4AC
4AC-150 engine on display at the San Diego Air & Space Museum
Type	Piston aircraft engine
National origin	United States
Manufacturer	Franklin Engine Company
First run	1938

The Franklin O-150 (company designation 4AC-150) was an American air-cooled aircraft engine of the late 1930s. The engine was of four-cylinder, horizontally-opposed layout and displaced 150 cu in (2 L). The power output was nominally 40 hp (30 kW).

Applications

• Aeronca 50 Chief
• Bartlett Zephyr
• Clutton-Tabenor FRED
• Fetterman Chickadee
• Payne MC-7 pusher
• Piper J-3 Cub
• Rose Parakeet
• Taylorcraft BF-65
• Taylorcraft L-2

Engines on display

• Aerospace Museum of California - Franklin 0-150 (4AC-150)

Specifications (4AC-150)

Data from Jane's all the World's Aircraft 1938.^[1]

General characteristics

• Type: 4-cylinder air-cooled horizontally opposed aircraft piston engine
• Bore: 3.625 in (92.1 mm)
• Stroke: 3.625 in (92.1 mm)
• Displacement: 149.6 cu in (2.45 L)
• Length: 27.5 in (70 cm)
• Width: 34.375 in (87.3 cm)
• Height: 18.375 in (46.7 cm)
• Dry weight: 155 lb (70 kg)

Components

• Valvetrain: Pushrod and rocker operated overhead valves. One intake, one exhaust
• Fuel system: Stromberg NA-S2 updraught carburetor
• Fuel type: 70 Octane gasoline
• Oil system: Wet sump full pressure system
• Cooling system: Air-cooled

Performance

• Power output: 40 hp (30 kW) at 1,875 rpm
• Compression ratio: 6.66:1
• Fuel consumption: 4.4 gal/h (17 L/h)
• Specific fuel consumption: 0.54 lb/hp/h