A number of changes were made for installing the 700 hp (520 kW) Curtiss V-1570 Conqueror engine.
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Powered by a 700 hp (520 kW) R-1750 Cyclone radial, its performance was dismal, despite retractable leading edge slots and large trailing-edge flaps, so a 600 hp (450 kW) Curtiss V-1570 Conqueror was substituted.
A myth surrounding the origins of the P-51 Mustang is linked to the North American Aviation (NAA) purchase of test data on the P-40 and P-46.
Testing with the R1820 was prolonged, so the Army's intention to promptly switch to a Curtiss V-1570 Conqueror engine and redesignate the aircraft XP-22 was dropped; another P-11 was chosen for that instead.