Uh, Goober,
Where did you hear a P-51 Mustang had a Pratt & Whitney 12 cylinder engine? Pratt & Whitney only made RADIAL ENGINES. The P&W R2800 was the engine of choise for many of the better fighters in WWII. It was used in the F6F Hellcat, the P-47 Thunderbolt, and the F4U Corsair. The P-51 Mustang was powered in the P51, P51A and A36 Apache versions with an Allison 1710, which is the same engine used in the P-38 Lightning and P-40 series. The P51 B/C and D/K versions used a Packard built Rolls Royce Merlin, as was used in the British Hurricane and Spitfire. I have to agree, though, that being next to a full sized unlimited hydro when the Merlin or Allison is started makes ANY CAR sound like a little .21.