SU HD6 carburettors Jaguar Mark X 3.8 - 1961-64, "Straight port" cylinder head, painted gold, 3 × SU HD8 carburettors Jaguar Mark 2 - 1959-67, "B type" cylinder head, painted dark blue metallic, 2 × SU HD6 carburettors Jaguar E-Type Series 1 3.8 - 1961-64, "Straight port" cylinder head, painted orange then gold, 3 × SU HD8 carburettors Jaguar S-Type 3.8 - 1963-68, "B type" cylinder head, dark blue metallic or later with smooth cam covers and unpainted, 2 × SU HD6 carburettors Panther J.72 3.0-litre 3-litre versions of the XK engine were built from 1959 onwards for FIA sports car racing with a 85 mm (3.35 in) bore and 88 mm (3.46 in) stroke. It was also popular with small race car manufacturers such as Lister Cars who could not afford to produce their own engines. As well as endurance racing, the engine was also used in Formula Libre racing. A 3.0-litre XK6 was used in the following road cars: Jaguar E2A prototype sports racer (1960) Jaguar E-type lightweight sports racer (1961) Jaguar D-type (non-works) sports racer (1959) Lister Cars endurance and formula racers Hersham and Walton Motors (HWM) endurance and formula racers Cooper Car Company endurance and formula racers John Tojeiro endurance and formula racers 4.2-litre A bored-out 4.2-litre version of the XK was officially released in 1964, although racers had been boring the 3.8 out to 4.2 litres for years. The factory 4.2-litre block was a new siamesed sleeve design which used respaced cylinders set evenly along the length of the block with new main bearing spacings and a new crankshaft. The middle two cylinders were moved closer together and the outer two moved further apart but the overall length of the block remained unchanged. This enabled the cylinder bores to be taken out to whilst retaining the familiar long stroke of for a total displacement of . Despite the re-spacing of the cylinder bores, the cylinder head castings remained unchanged. As a result, the centrelines of the combustion chambers in the head no longer aligned precisely with the centrelines of the cylinders but this did not matter greatly as the combustion chamber diameters in the head were smaller than the cylinder diameters. The 3.8 and 4.2-litre cylinder heads and cams are therefore interchangeable. The 4.2-litre engine from the factory had unsmoothed steps between the inlet manifold and head, and the manifold gaskets were not a good