The FIAT Mefistofele (sometimes known simply as Mefistofele) is a one-off racing car created by Ernest Eldridge by combining a Fiat racing car and aeroplane engine in 1923. It is named after the demon Mephistopheles, a decision inspired by the infernal noise emitted from the unmuffled engine.
The Mephistopheles was created by combining the chassis of the 1908 Fiat SB4 with a 6-cylinder, 21.7 litre (21706 cc) Fiat A.12 aeroplane engine producing 320 PS (235 kW; 316 bhp).
The engine named Fiat A.12 is a six-cylinder liquid-cooled in-line engine with a bore of 160 mm and a stroke of 180 mm, giving a capacity of 21,7 litre, with variants producing between 245 and 300 horsepower at 1,700 rpm. The A.12 was a large aero engine at the time and its dimensions were more typical of a marine engine, but it was efficient and reliable. It is to be assumed that Fiat's prior experience with extremely large racing engines contributed to its success. A total of 13,260 A.12s were produced between 1916 and 1919.