| Continued from above… We have all three of the Merlin series Blueprints. This blueprint is the Rolls Royce Merlin XX/ V-1650 Packard 28, the second in the series. (Merlin XX/ V-1650 Packard 28: Single-stage, two-speed gearbox) The Merlin was considered to be so important to the war effort that negotiations soon started to establish an alternative production line outside the UK. Agreement was reached with the Packard company in Detroit in September 1940, and the first Packard-built engine, designated V-1650-1, ran in August 1941. The first American production of the Merlin was the Packard Merlin 28 or the equivalent of the Rolls Royce Mark XX. This engine was a ((single stage, two speed supercharger)). This engine (Merlin 28) was used for the Lancaster bomber. The USAAF version of this engine was designated the V-1650-1 which were also used on the P-40F's. The initial Packard modification on the Merlins were done on this engine by changing the main bearings from a copper lead alloy to a silver lead combination and featured indium plating. Indium plating had been developed by the General Motors (Pontiac Division) to prevent corrosion which was possible with lubricating oils that were used at that time. The bearing coating also improved break-in and load carrying ability of the surface. British engineering staff assigned to Packard were astonished at the suggestion but after tear down inspections on rigidly tested engines they were convinced the new design offered a decided improvement.
As the Merlin evolved so too did the supercharger; fitting into three broad categories:
| - Single-stage, single-speed gearbox: Merlin I to III, XII, 30, 40, and 50 series
- Single-stage, two-speed gearbox: Merlin X, Merlin XX
- Two-stage, two-speed gearbox: Merlin 60, 70, 80 and 100 series
(Photo left: Courtesy of AirArchive.com) |  | Most of the Merlin engine's technical improvements resulted from more efficient superchargers and fuel with increased octane ratings...
Between 1939 and 1945 the Merlin saw operational service in more then 18 different types of aircraft plus large families of Spitfires and Mosquitos. A major design change to the supercharger coupled with high-octane fuel resulted in increased power output. Ratings in service ranged from 1,000 hp. to over 2,000 hp (Merlin 66, 1944). The engine was also produced post war for civil aircraft. Merlin production at Rolls-Royce was shared by Ford in the U. K. and Packard and Continental in the United States. A total of 168,000 Merlin engines were built, with over 55,000 of these in the USA between 1941 and 1945.
Still considered by many historians; "one of the finest piston engines ever conceived". | | 
