The Jaguar XK is an inline 6-cylinder dual overhead camshaft (DOHC) engine produced by Jaguar Cars between 1949 and 1992. Introduced as a 3.4-litre, it earned fame on both the road and track, being produced in five displacements between 2.4 and 4.2-litres for Jaguar passenger cars, with other sizes being made by Jaguar and privateers for racing. A de-rated version was also used in certain military vehicles built by Alvis and Daimler. Early development Prior to World War II, SS Cars (which changed its name to Jaguar in 1945) used three engines produced by the Standard Motor Company: a 1.5-litre 4-cylinder and 6-cylinder engines of 2.5 and 3.5 litres. Sir William Lyons and his engine designers; William Heynes (Chief Engineer), Walter Hassan, Claude Baily, and Harry Weslake are widely reported to have discussed a new range of replacements whilst fire-watching on the roof of the SS factory in Swallow Road, Coventry, during German World War II bombing raids. Rather than developing prototype engines immediately after the war, it is claimed that Jaguar's wartime engine developments went far beyond mere discussion and design, extending to the construction and testing of several prototype engines as early as 1943. The initial aim was to produce a series of engines of higher than normal output that would be able to stay ahead of the competition without revision for many years and which Sir William insisted also had to "look good". In 1942-43, a range of configurations was considered and it was concluded that, for good breathing and high bmep, the new engines would need vee-opposed valves operating in hemispherical combustion chambers. Two configurations of this type were selected for comparison in 1943 and the prototypes named "XG" and "XF". The XG 4-cylinder of 1,776 cc, first tested in October 1943, was based on the 1.5-litre Standard block and used its single cam-in-block to operate the opposed valves via a complicated crossover pushrod arrangement, similar to that of the pre-war BMW 328. The XF 4-cylinder of 1,732 cc used the now familiar dual overhead cam (DOHC) configuration and was first tested in November 1944. The XG was found to suffer from excessive pushrod and rocker noise and gas flow figures through its vertical valve ports did not equal those of the horizontal ports on the XF. Therefore, from these two options, the DOHC XF layout was selected. 4-cyl engine development progressed as follows: XG Pushrod