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they are both Rolls Royce engines
I don't think so. The Allison V-1710 (1710 C.I.) was a completely different engine from the Rolls-Royce Merlin. The V-1710 was on of the first American liquid-cooled V12s mass-produced. It powered such planes as the P-40 Tomahawk/Kittyhawk, P-38 Lightnings, and early A-36 Apache/P-51 Mustang models. Early versions were non-supercharged (in the P-40 and A-36/P-51A) thus having good power output but dropping off above 20,000'. In later versions the V1710 was supercharged, capable of 1600 HP and could propel a P-38 to 420 MPH at 25,000'.