Wright R - 3350 Duplex - Cyclone The Wright R - 3350 Duplex - Cyclone was one of the most powerful radial aircraft engines produced in the United States . It was a twin row , supercharged , air - cooled , radial engine with 18 cylinders . Power ranged from 2 , 200 to over 3 , 700 hp ( 1 , 640 to 2 , 760 kW ) , depending on the model . Developed before World War II , the R - 3350 ' s design required a long time to mature before finally being used to power the Boeing B - 29 Superfortress . After the war , the engine had matured sufficiently to become a major civilian airliner design , notably in its Turbo - Compound forms . The engine is now commonly used on Hawker Sea Fury and Grumman F8F Bearcat Unlimited Class Racers at the Reno Air Races . Design and development . In 1927 , Wright Aeronautical introduced its famous " Cyclone " engine , which powered a number of designs in the 1930s . After merging with Curtiss to become Curtiss - Wright in 1929 , an effort was started to redesign the engine to the 1 , 000 hp ( 750 kW ) class . The new Wright R - 1820 " Cyclone 9 " first ran successfully in 1935 , and would become one of the most used aircraft engines in the 1930s and World War II , powering all frontline examples ( the - C through - G models ) of the legendary B - 17 Flying Fortress Allied heavy bomber aircraft to serve in the war , each powerplant assisted by a General Electric - designed turbocharger for maximum power output at high altitudes . At about the same time Pratt & Whitney had started a development of their equally famous Wasp design into a larger and much more powerful two - row design that would easily compete with this larger Cyclone . In 1935 Wright decided to follow P & W ' s lead , and started to develop much larger engines based on the mechanicals of the Cyclone . The result were two designs with a somewhat shorter stroke , a 14 cylinder design that would evolve into the Wright R - 2600 , and a much larger 18 cylinder design that became the R - 3350 . An even larger 2 - row 22 cylinder version , the R - 4090 , was experimented with as a competitor to the P & W R - 4360 but was not produced . The first R - 3350 was run in May 1937 . Continued development was slow , both due to the complex nature of the engine , as well as the R - 2600 receiving considerably more attention . The R - 3350 didn ' t fly until 1941 , after the prototype Douglas XB - 19 had been re - designed from the Allison V - 3420 to the R - 3350 . Things changed dramatically in 1940 with the introduction of a new contract by the USAAC to develop a long - range bomber capable of flying from the US to Germany with a 2 , 000 lb ( 900 kg ) bomb load . Although smaller than the Bomber D designs that led to the B - 19 , the new designs required roughly the same amount of power . When preliminary designs were returned in the summer of 1940 , three of the four designs were based on the R - 3350 . Suddenly the engine was seen as the future of Army aviation , and serious efforts to get the design into production started . By 1943 the ultimate development of the new bomber program , the Boeing B - 29 Superfortress , was flying . However the engines remained temperamental , and showed an alarming tendency of the rear cylinders to overheat , partially due to minimal clearance between the cylinder baffles and the cowl . A number of changes were introduced into the aircraft production line in order to provide more cooling at low speeds , with the aircraft rushed into operational use in the Pacific in 1944 . This proved unwise , as the early B - 29 tactics of maximum weights combined with high temperatures of the tropical airfields where B - 29s were based , produced overheating problems that were not completely solved , and the engines had a tendency to swallow their own valves . Because of a high magnesium content in the potentially combustible crankcase alloy , the resulting engine fires - sometimes burning with as high a core temperature approaching 5 , 600 °F ( 3 , 100 °C ) from the Duplex Cyclone ' s magnesium engine crankcase alloys - were often so intense the main spar could burn through in seconds , resulting in catastrophic wing failure . Early versions of the R - 3350 had carburetors , though the poorly designed elbow entrance to the supercharger led to serious problems with fuel / air distribution . Near the end of World War II , the system was changed to use direct injection where fuel was injected directly into the combustion chamber . This change improved engine reliability . After the war the engine was redesigned and became a favorite for large aircraft , notably the Lockheed Constellation and Douglas DC - 7 . Following the war the Turbo - Compound system was developed to deliver better fuel efficiency . In these versions , three power recovery turbines ( PRT ) were inserted into the exhaust piping of each group of six cylinders and geared to the engine crankshaft by fluid coupling s to deliver more power . The PRTs recovered about 20 percent of the exhaust energy ( around 450 hp ) that would have otherwise been wasted , but reduced engine reliability . The fuel burn for the PRT equipped aircraft was nearly the same as the older Pratt and Whitney R - 2800 , while producing more horsepower . Effective 15 October 1957 a DA - 3 / DA - 4 engine cost $ 88 , 200 . By this point reliability had improved with the mean time between overhaul s at 3 , 500 hours and specific fuel consumption in the order of 0 . 4 lb / hp / hour ( 243 g / kWh , giving it a 34 % fuel efficiency ) . Engines in use now are limited to manifold pressure , being 2 , 880 hp with 100 / 130 octane fuel ( or 100LL ) instead of the and 3 , 400 HP possible with 115 / 145 , or better , octane fuels , which are no longer available . Several racers at the Reno Air Races use R - 3350s . Modifications on one , Rare Bear , include a nose case designed for a slow - turning prop , taken from a R - 3350 used on the Lockheed L - 1649 Starliner , mated to the power section ( crankcase , crank , pistons , and cylinders ) taken from a R - 3350 used on the Douglas DC - 7 . The supercharger is taken from a R - 3350 used on the Lockheed EC - 121 and the engine is fitted with Nitrous Oxide injection . Normal rated power of a stock R - 3350 is 2 , 800 horsepower at 2 , 600 rpm and 45 inches of manifold pressure . With these modifications , Rare Bear ' s engine produces 4 , 000 horsepower at 3 , 200 rpm and 80 inches of manifold pressure and 4 , 500 horsepower with Nitrous Oxide injection .