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 R for the 1931 race, modified as an S.6A) does not contain an R engine. Rolls-Royce R The Rolls-Royce R was a British aero engine designed and built specifically for air racing purposes by Rolls-Royce Limited. Nineteen R engines were assembled in a limited production run between 1929 and 1931. Developed from the Rolls-Royce Buzzard, it was a 37-litre (2,240 cu in) capacity, supercharged V-12 capable of producing just under 2,800 horsepower (2,090 kW), and weighed 1,640 pounds (770 kg). Intensive factory testing revealed mechanical failures which were remedied by redesigning the components, greatly improving reliability. The R was used with