I'm surprised at the number people who don't know the P40D (I think), F and L were in fact Merlin powered. Albeit the same Merlin that powered the Spitfire V IIRC.
As far as I know, it boosted the Warhawks performance to a respectable 364 mph at 20,000 feet thanks to it's 1 stage, 2 speed supercharger versus the single speed, single stage supercharger of the Allison powered E that topped out at around 340 at 15,000 feet.
Any thoughts and info? Please feel free to correct any errors I may have made.
Edit:
Well that didn't take long.
The P40 F had a Merlin 20 series engine while the Spit mk.V had a Merlin 45 series. Big thanks to Wwuzak
for pointing that out.
And a P40D airframe was fitted with a Merlin as an experiment, not starting with the D model. My mistake.