The R-3350 was one of the most powerful radial engines produced in the United States. Using 18 cylinders of the R-2600, gave it a displacement of 3,342 cubic inches. The crucial application was for the Boeing B-29.
The R-3350 was first run in 1937. The earliest flight I can find is on the XB-19 in 1941. The Cyclone 18 became the engine of choice for large military and civilian aircraft into the 1950s.

Some later versions of the R-3350 were produced as "turbo compound" engines. Three exhaust driven turbines converted about 20% of the exhaust gas heat energy into useful power. These turbines drove a gearing mechanism that added power to the engine crankshaft.

models

• R-3350-23: 2,200 hp (1641 kW) with turbocharger R-3350-26B: 2,800 hp (2088 kW)
• R-3350-32W: 3,500 hp (2610 kW) turbo-compound
• R-3350-34: 2,200 hp (1641 kW)
• R-3350-85: 3,500 hp (2610 kW)
• R-3350-91: 3,250 hp (2424 kW)

specifications

• 18 cylinder, air-cooled, two-row radial
• displacement: 3,342 cubic inches (54.8 litres)
• bore x stroke: 6.125 x 6.3125 inches

used by

• Douglas AD-1 Skyraider
• Boeing B-29 Superfortress
• Lockheed L-49/C-69 Constellation
• Fairchild C-119 Flying Boxcar
• Lockheed L-749/C-121 Constellation
• Lockheed P2V Neptune