This is a Rolls Royce PV-12 AKA Merlin from a P-51 Mustang. these powerful engines were used mostly in english aircraft such as the spitfire, hurricane, and the lancaster. the british installed this motor in the P-51's and a few P-40's. this is an awesome engine and is still a favorite powerplant in the reno air races. after WWII these engines were also installed in ME-109's the former enemies of the original carriers.