 The airframe itself was strengthened, with the fuselage and engine mount area receiving more formers because of the greater weight of the Packard V-1650-3 compared with the V-1710.The engine cowling was completely redesigned to house the Packard Merlin, which, because of the intercooler radiator mounted on the supercharger casing, was taller and used an updraft carburetor, rather than the downdraft variety of the Allison.The new engine drove a four-bladed -diameter Hamilton Standard propeller that featured cuffs of hard molded rubber.