General Motors X-250, Radial 4 (8) Engine

Type: Radial, 4 (8) cylinders, supercharged, liquid-cooled

Power rating: 168 kW (225 hp) at 2,500 rpm

Displacement: 4.1 L (252 cu in)

Bore and Stroke: 78 mm (3.0625 in.) x 109 mm (4.281 in.)

Weight: 125 kg (275 lb)

A direct-drive, liquid-cooled, supercharged, two-stroke cycle engine, this General Motors engine was a very unusual design incorporating four cylinder blocks, each containing two cylinder bores with a common combustion chamber. At least one application was a small radio controlled target aircraft, and it also powered an Oldsmobile Eight automobile. Flight testing by famed racing and test pilot Tony LeVier successfully continued through 1940 as high as 7.6 km (25,000 ft.) in a Cessna Airmaster C-165, but other pressing war priorities led to termination of the project.

A 1942 engineering report written by GM's Research Laboratories, led at the time by its highly regarded director Charles F. Kettering, stated that the engine had excellent power/displacement and power/weight ratios, low fuel consumption, and very low vibration characteristics.

Removed from the Cessna in June 1946, the aircraft was later refurbished and flown again.