XP-47J

A Republic XP-47H Thunderbolt fitted with a liquid-cooled engine; note revised forward fuselage.(rudeerude)

Republic XP-47H 

From wikipedia

The XP-47J began as a November 1942 request to Republic for a high-performance version of the Thunderbolt using a lighter airframe and an uprated engine with water injection and fan cooling. Kartveli designed an aircraft fitted with a tight-cowled Pratt & Whitney R-2800-57(C) with a war emergency rating of 2,800 hp (2,090 kW), reduced armament of six 0.50 in (12.7 mm) machine guns, a new and lighter wing, and many other changes. The only XP-47J was first flown in late November 1943. When fitted with a GE CH-5 turbosupercharger, the XP-47J achieved a top speed of 505 mph (440 kn, 813 km/h) in level flight in August 1944, making it one of the fastest piston engine fighters ever built. However, by that time Republic had moved on to a new concept, the XP-72.(rudeerude)