Isotta Fraschini produced a long series of engines with the name Asso (Ace, in English). The Asso XI.RC was an upright, liquid-cooled V-12 engine with maximum power output in the range 670-725 kW (900-970 hp) depending on the degree of supercharging. There were two variants, differing only in their supercharger speed: the R.C.40 ran at a little over 10 times the crankshaft speed and enabled the engine to maintain a rated power of 623 kW (836 hp) to an altitude of 4,000 m (13,120 ft) (hence the 40 in the variant name) whereas the R.2C.15 held 655 kW (880 hp) to 1,500 m (4,920 ft) with a supercharger gearing of 7.
All variants of the RC.40 had much in common constructionally with the earlier Asso-750.RC, though they had two, rather than three, banks of 6 cylinders and 4 rather than 2 valves per cylinder. Cylinder barrels were machined from carbon steel with flat-topped heads and valve seatings. Each barrel had a separate sheet steel water jacket. Cast aluminium head blocks were bolted to each of the two banks of 6 cylinders, providing valve ports, guides, coolant passages and camshaft supports. The pistons were also aluminium castings. The crankshaft was a 6-throw design with 8 plain bearings and a double row ball thrust bearing between the front two. The connecting rods had bronze bush little ends and white metal big ends. The crankcase was cast in two parts, the upper one with the housings for the crankshaft bearings.
Valvetrain: Two intake and two exhaust valves per cylinder, drive via cams and T-shaped tappets from inlet and exhaust pairs of overhead camshafts geared together, one for each bank of 6 cylinders, each pair driven by its own shaft connected indirectly to the crankshaftbevel gear.
Supercharger: Single speed, single stage centrifugal, running at 10.714 times crankshaft speed.