つか英語版に説明あった
https://en.wikipedia.org/wiki/List_of_Curtiss_P-40_Warhawk_variants

"The P-40K was essentially a P-40E with a significantly higher rated Allison engine in it,
the V-1710-73 rated at 1,325 hp for takeoff and 1,550 hp for War Emergency Power (for 5 minutes) at Sea Level."

"The P-40N featured a lengthened fuselage and a more powerful 1300 hp Allison engine
but the use of a single speed, single stage supercharger gave the model only a marginally better effective altitude than a P-40E.
As with the F/L, there were both 'light' and 'heavy' versions, the lightest 'hot' fighter-configuration-with-four-guns P-40Ns achieved a top speed of up to 378 mph. "