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 V8 engine the L410I, denoting fuel injection, the L410IT (for Injection Turbo) and the L410ITI (for Injection Turbo Intercooler). 94MY (model year) saw the introduction of a serpentine drive belt front-end, revised combustion system and an integrated engine cover. Developments of the L410 continued in production to power Rolls-Royces and Bentleys until the adoption of BMW V12 power by Rolls-Royce in the Silver Seraph and, subsequently, after BMW was granted a license to use the Rolls-Royce brand (for automobiles) in the Goodwood-produced Phantom. The L410 engine is still used by Bentley well into the 21st century, having been brought back into production