Pratt & Whitney X-1800

The Pratt & Whitney X-1800 H-2600, was a American aircraft engine project. It was a watercooled 24-cylinder H-block of 2,597.7in³ (42.57 liters)(5.25" x 5.0"). It was intended to be used in the Vultee XP-54, Curtiss-Wright XP-55, Northrop XP-56, and Lockheed XP-49. Projected performance was to be 1,800 to 2,200 hp (1850-2200 PS, 1350-1640 kW), with a turbocharger to secure high-altitude performance.

The target date for series production was 1942. In 1940, however, performance on the test bench did not continue to improve, demonstrating a need for considerable additional development effort. P&W subsequently ended development of the X-1800 in October 1940, with only one built, to concentrate on radials.

An enlarged version, the H-3130, displaced 3732.22in³, from a bore and stroke of 6.0" x 5.5". Power was estimated to be 2650 but this engine was also cancelled.