The V-770 was an inverted V-12 air cooled aircraft engine developed for use in US Aircraft during World War II. The engine had a displacement of 773 cu in, bore of 4 inches, stroke of 5.125 inches and a compression ratio of 6.5:1.  The V-770-11 engine illustrated weighed 730 lbs, measured 62 inches in length with a width of 28 inches and height of 32.25 inches, and delivered 520 hp at 3,000 rpm.
First flown in 1931, the engine was designed to use 87 octane fuel. Apart from the Bell XP-77, use of the V-770 appears to have been limited to the Fairchild AT-21 gunnery training aircraft.
↑ 1.01.1Gunston, Bill (Forward). Jane's Fighting Aircraft of World War II. Tiger Books. 1989. ISBN 1-85501-996-5. (Reprint of Jane's All The World's Aircraft 1945/1946. Bridgeman, Leonard (Editor). 1946).