the Jaguar 3.4-litre. The designation "Mark 1" for these cars was applied retrospectively, after the release of the Mark 2 in 1959. The original 3.4-litre XK6 was used in the following road cars: Jaguar XK120 - 1948-53, "Standard (or "A type")" cylinder head, bare aluminium finish, 2 × SU H6 carburettors. The XK 120 C came with the C-type head (red) as an option from 1951 to 1952 with 2 × SU H8 carburettors. In 1953, the XK 120 C switched to a triple 40 DCOE Weber carburetor setup. The XK 120 SE and M came with the C-type head as an option with 2 × SU H6 carburettors (occasionally SU H8) Jaguar XK140 - 1954-57, "Standard (or "A type")" cylinder head, 2 × SU H6 carburettors. The XK 140 SE or M came with the C-type head as an option, painted red with 2 × SU H6 or H8 carburettors Jaguar XK 150 3.4 - 1957-61, "B type" cylinder head, painted light blue-green, 2 × SU HD6 carburettors Jaguar XK 150 3.4S - 1957-61, "Straight port" cylinder head, painted orange, 3 × SU HD8 carburettors Jaguar Mark VII - 1950-54, "A type" then "C type" (as option from April 1953) cylinder head, unpainted aluminium, 2 × SU H6 carburettors Jaguar MkVIIM - 1954-57, "C type" cylinder head, 2 × SU H6 carburettors, some had high-lift cams Jaguar Mark VIII - 1956–1958, "B type" cylinder head, painted light blue-green, 2 × SU HD6 carburettors Jaguar 3.4-litre 'Mark 1' - 1957-59, "B type" cylinder head, painted light blue-green, 2 × SU HD6 carburettors Jaguar 3.4-litre Mark 2 - 1959-67, "B type" cylinder head, painted light blue-green, 2 × SU HD6 carburettors Jaguar 340 Mark 2 - 1967-68, "B type" cylinder head, ribbed cam covers, 2 × SU HD6 carburettors Jaguar S-Type 3.4 - 1963-68, "B type" cylinder head painted light blue-green, smooth cam covers, 2 × SU HD6 carburettors 2.4-litre In the mid-1950s, Jaguar lacked a compact saloon of the type represented until 1949 by the Standard-engined 1½ litre. In choosing a power unit for its all new compact saloon, Jaguar could choose between the 1,995 cc four-cylinder XK prototype and a downsized version of the 3.4-litre six-cylinder XK. The 4-cylinder was considered too low powered and unrefined. The 3.4 was already well "undersquare", which means that its bore was much less than its stroke, so a smaller bore version of