 It was quickly evident that performance, although exceptional up to 15,000 ft (4,572 m), was inadequate at higher altitudes.This deficiency was due largely to the single-stage supercharged Allison engine, which lacked power at higher altitudes.Still, the Mustang's advanced aerodynamics showed to advantage, as the Mustang Mk.I was about 30 mph (48 km/h) faster than contemporary Curtiss P-40 fighters using the same Allison powerplant.