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 20/25 Best timed speed: 76.27 mph Maximum Speeds in gears: Petrol Consumption: Driven Hard – 14 mpg The 20/25 engine and chassis were designed for the owner driver market – ideally fitted with a smaller sedan or coupe body as the one used in the 1935 Autocar Test. Unfortunately many 20/25’s were fitted with larger and heavier limousine bodies which hurt their performance. Only the chassis and mechanical parts were made by Rolls-Royce. The body was made and fitted by a coachbuilder selected by the owner. Amongst the most respected coachbuilders who produced bodies for Rolls Royce cars are Park Ward,