2,100 hp (1,566 kW) at 2,800 rpm at 1,000 ft (305 m); 1,800 hp (1,342 kW) at 2,800 rpm at 25,500 ft (7,772 m).[19] First series production variant of the "C" Series, which was a complete redesign of the R-2800. Some of the main changes were forged, rather than cast cylinders, allowing an increased compression ratio (from 6.65:1 to 6.75:1), a redesigned crankshaft, a single piece, rather than split crankcase center section, and a two section nose casing, incorporating hydraulically operated torque-monitoring equipment and an automatic, vacuum operated spark-advance unit.[20] The supercharger used fluid coupling for the second stage.[21] Updraft Bendix-Stromberg PT-13G2-10 carburetor. Used in Vought F4U-4 and -4 variants.[nb 5] Production = 3,257 (P&W).[23]