Hispano Suiza V8 by the Wright-Martin Aircraft company.

 At the beginning of WW1 the German Mercedes aero engine was known to be better than anything the Allies were producing, and a search for a good engine to produce as a standard powerplant led to the Hispano Suiza water-cooled SOHC V8 to be chosen, producing good power while being light and manufacturable. Production started at the Paris factory in late 1915 and soon was being made in many different factories in several countries. 
In early 1916 General Aeronautics in America landed a contract for 450 engines. A year later only 100 engines had been delivered, and changes were needed. The company reorganized as the Wright-Martin Aircraft company, learned to make the intricate aluminum castings and to do the advanced machining required and production improved. 
In Europe the engine was being developed to produce more power and Wright Martin, unable to get full specifications, started their own program and by the Armistice in November 1918 the first 300 hp engine was on the test stand. The 150 hp engine was used in the Curtiss Jenny and the by the early 1920s the 300 hp version had been developed into one of the best pursuit plane engines.