Franklin O-150

 Herbert Franklin developed aluminum die-casting in 1895, and by 1902 had begun to manufacture lightweight automobiles using air-cooled aluminum engines. Franklin Automobile Company became a victim of the Depression and was purchased by several former engineers. They formed Aircooled Motors Corporation of Syracuse, New York in 1935. They supervised the design of the Franklin Model 4AC-150 air-cooled engine that was announced early in 1938. The engine was used on such aircraft as the Aeronca 50-F, Piper J-3F Cub and the Taylorcraft BF.
During WW2 and throughout the 1950s and 1960s, Franklin specialized in helicopter engines. Versions of their engines were offered for horizontal mounting and vertical mounting. The company built 2, 4, 6, 8 and 12-cylinder engines, although many of these did not see production.
In 1975, the company disbanded and sold all rights to the Polish government, becoming part of PZL, an association of Polish aero and engine manufacturers.
The Franklin O-150 (company designation 4AC-150) was an air-cooled aircraft engine of four-cylinder, horizontally-opposed layout that displaced 150 cu in (2 L). The power output was nominally 40 hp (30 kW). The first model used a single magneto. Later engines were offered with a reduction gearing that shifted to direct drive for cruise.

Technical Details:

Engine: 4-cylinder, air-cooled, horizontally-opposed
Power: 40 hp (30 kW) at 1,875 rpm
Weight: 155 lb (70 kg)
Cylinders: bore 3.62 in (92 mm), stroke: 3.62 in (92 mm)
Displacement: 149.6 cu in (2.45 L)
Compression ratio: 6.66:1
Fuel consumption: 4.4 US gal/hr (17 L/h)