The M-103 was a further development of the Klimov M-100 engine that was itself a licensed copy of the French Hispano-Suiza 12Ybrs. It differed from both engines in a number of aspects such as increased compression ratio, increased supercharger ratio, increased rpm's, strengthened cylinder blocks, a new crankshaft, a more aggressive camshaft, and flat bottomed cylinders. Developed in 1936 it was ready for testing in October 1936. The first two models failed testing due to cracked cylinder blocks and the engine was resubmitted for testing in 1937. After passing its trials it was cleared for production in 1938 and 11,681 were produced until 1942 at its factory in Rybinsk. The M-103 was followed by the M-105.
Supercharger: Gear-driven single-speed centrifugal type compressor. Gear ratio: 11.0:1. Maximum boost for take-off: 1,100 mm Hg (43.30 MP). Maximum boost at altitude: 920 mm Hg (36.22 MP). Critical altitude: 4,000 m (13,123 ft)
Fuel system: Six K-100A Carburettors (License copy of Solex-Hispano 56S2 self-adjusted carburettor)
Fuel type: 90 (minimum grade), 95 or 100 octane.
^Valtion Lentokonetehdas (1943). Hispano-Suiza 12Y-31, M-103, M-105. Rakenneselostus, Käyttö – Ja Huoltoohjeet [“Valtion Lentokonetehdas” State Aircraft Factory: Hispano-Suiza 12Y-31, M-103, M-105. Use and Maintenance Instructions.] Helsinki: Maintenance and spare technical manual of the Finnish Government. The National Library of Finland.
^During the war, the Soviet Air Force used automotive gasoline and all kind of mixtures without troubles.