"...The big V16 was rated at 2,500 hp (1,900 kW). It was finally tested in June 1945. It was installed in the P-47 Thunderbolt in place of a radial engine. This airplane was designated the XP47H. The change in engine and aerodynamics increased the top speed from 439 mph (707 km/h) to 504 mph (811 km/h).." tracked by radar at altitude. In the back of a Mopar mag. Republic XP-47J (a variant of the P-47 Thunderbolt) reached 813 km/h (505 mph) in testing (wikipedia, not really trustworthy unless the J pictured was still a radial), And "Contra-rotating" is correct.