during a search of some types of military vehicles, I explored the biography of Dante Giacosa (known for being the "father of the 500"). Eng. Giacosa was one of the directors of FIAT technical staff and he was also involved in aircraft engines. In his autobiography, albeit with some imprecision, we read that in 1940-1942 the Department of the Air demanded an airplane engine with high performance and Eng. Antonio Fessia named Eng. Carlo Felice Bona, Director of the Avio Engines, in charge of the development. This engine was to have a V16 layout and deliver 2,000 hp at 8,000 m.
I think he was talking about the A.44 RC.15/45.
But Eng Giacosa thought that his staff could provide an alternative configuration and designed a 24-cylinder X engine with four banks of six cylinders each (at 90°), compatible with a 20 mm cannon or a 12,7 mm machine gun firing through the propeller shaft. The engine was called FIAT A.40 (I never heard of before) and technical drawings are dated January 22, 1943. No photographs are known. Giacosa says that two prototypes were built but never bench-tested.
Of this unknown engine Giacosa includes two views that I attach.
Anyone of you knows something about it?