Rolls-Royce Merlin exhaust flow and waste-gates, meant that this option was rejected in favour of the two-stage supercharger. Fitted with the two-stage two-speed supercharger, the Merlin 60 series gained 300 horsepower (224 kW) at over the Merlin 45 series, at which altitude a Spitfire IX was nearly faster than a Spitfire V. The two-stage Merlin family was extended in 1943 with the Merlin 66 which had its supercharger geared for increased power ratings at low altitudes, and the Merlin 70 series that were designed to deliver increased power at high altitudes. While the design of the two-stage supercharger forged ahead, Rolls-Royce also
Rolls-Royce–Bentley L-series V8 engine known as the B61. The need for a new engine was recognised by Rolls Royce in the early 1950s and its development began in 1952, bearing no relation to the 1905 Rolls-Royce V8. The result was a series of V8 engines known as the L series, more specifically the "L410" for its bore size of , in keeping with company practice. Developments of the L410 continued in production powering Rolls-Royces up to 1998 and Bentleys into the 21st century. Bentley, under Volkswagen ownership since 1998, continues to develop the L410 for its range of cars. Roll-Royce ceased using the L410