Pratt and Whitney Engines 1937 - USA
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	Twin Wasp's displacement was 1,830 cubic inches. It produced 1,000 hp at 2,600 rpm for takeoff.

Pratt & Whitney Aircraft, East Hartford, Conn., the engine manufacturing division of the United Aircraft Corporation, produced and delivered approximately 1,300 engines during 1936. All were in the higher horsepower classification, ranging from the 420 hp Wasp Junior to the 1,000 hp Twin Wasp. The total number of engines produced since the organization of the company in 1925 exceeded 11,000. Basically, two types of Pratt & Whitney radial air-cooled engines were in current production, at the beginning of 1937--the nine cylinder single-row type and the 14 cylinder double-row type. Included in the first group are the Wasp Junior, the Wasp and the Hornet, and in the second, the Twin Wasp Junior and the Twin Wasp. Improvements in all those models made possible higher horsepower ratings both for take-off and for cruising. Considerable development in the double-row engine type was announced during the year at the time when the 1,000 hp Twin Wasp was offered for service. This development period extended back to 1929 when the company first began its double-row engine experimentation. Much interest for both commercial and military service has been shown in Pratt & Whitney's two double-row engines, and more than 1,000 of them have gone into service to date. The company stated that "advantages of the double-row power plant for aircraft are evident. Large displacement is possible with no increase, but actually a substantial decrease, in frontal area. This lends itself to plane design whether it be multi-engine or single-engine. The use of smaller cylinders permits greater crank speeds which in turn contribute to smooth operation and the smaller, more frequent power impulses further contribute to smoothness and long life." Distinctive and exclusive design features of current Pratt & Whitney engines included completely automatic valve gear lubrication, automatic mixture control, and improved cylinder head finning, which together with patented pressure baffles, provided maximum cooling and minimum fuel consumption. The policy of the company was based on the belief that future requirements for both military and commercial service will call for more horsepower than was available in 1936. Pratt & Whitney announced that the two-row type has the same possibilities for future development as the single row engine had a decade ago, and company engineers were working on the development and test of larger models of the two-row engine. Basically, Pratt & Whitney engines were divided into five distinct groups: The Wasp Junior, Wasp, Hornet, Twin Wasp and Twin Wasp Junior. In each engine group there were a number of different engines, each with a separate rating, but the general specifications of all engines in each group were identical. While Pratt & Whitney's available engine list contained a large number of units not referred to here, nevertheless, those which are discussed were the latest models appearing on their current production list at the beginning of 1937. The Wasp Junior had a displacement of 985 cubic inches, an overall diameter of 46-3/4 inches, and a bore and stroke of 5-3/16 inches. It could be had with either a geared or direct drive, the former weighing 800 pounds bare and the latter 596 pounds bare. The geared form, Model SC-G, the company reported, produced for take-off 600 hp at 2,850 rpm and delivered 525 hp at 2,700 rpm at 8,000 feet as a maximum power for continuous cruising. It had an overall length of 45-3/4 inches, a compression ratio of 6.7:1, and a blower ratio of 11:1, and 87-octane fuel is specified. Model SB was a direct drive Wasp Junior delivering 450 hp at 2,300 rpm for takeoff. Its maximum power for continuous operation was 400 hp at 2,200 rpm at 5,000 feet. Its overall length was 42-1/8 inches, compression ratio 6:1, blower ratio 10:1 and fuel specification 87-octane. Model TB was rated at 420 hp at 2,200 rpm at sea level and operated on 80-octane fuel, with a compression ratio of 6:1 and a blower ratio of 8:1.

The Wasp model SIHI-G provided 600 horsepower at 2,250 rpm with a displacement of 1,344 cubic inches.