The Ducati 851 was the first Ducati to use a liquid-cooled four-valve-per-cylinder engine.
Introduced for the 1987 model year, the 851 marked a major technical shift for Ducati. Its 851 cc V-twin used liquid cooling and four desmodromically actuated valves per cylinder, while electronic fuel injection helped deliver the performance needed for modern superbike competition.
The engine was designed under Massimo Bordi and developed with racing in mind. Ducati's later 888 and 916 became more famous, but both built on the architecture and lessons established by the 851.
The 851 is sometimes confused with the 750 F1, which preceded it and used an air-cooled two-valve engine. The model number refers broadly to engine displacement rather than the number of cylinders or valves.