What engine was used in the aircraft intended to replace the F4F Wildcat?
Republic P-47 Thunderbolt:  The P-47 was designed around the powerful Pratt & Whitney R-2800 Double Wasp engine which was also used by two U.S. Navy fighters, the Grumman F6F Hellcat and the Vought F4U Corsair. Grumman F6F Hellcat:  Designed to replace the earlier F4F Wildcat and to counter the Japanese Mitsubishi A6M Zero, it was the United States Navy's dominant fighter in the second half of the Pacific War.
Pratt & Whitney R-2800 Double Wasp engine