A R. R. Merlin Engine,  no not in a Merc. but in a P51 Mustang  Had great Aerodynamics, but lost Power after 14,000 feet..... A Merlin Engine to the rescue... good for 35000 feet... 
Then was 20 MPH faster than a Spitfire same Engine.... Widest part of the Wing was 2 thirds along 
Spitfire was near the Tip. less drag.
 Merlin was made under licence by Packard, better than the original UK Engines.