the 3.4 was not seen as a realistic proposition. Jaguar was therefore obliged to create a short-stroke version of the 6-cylinder XK with a shorter cylinder block, reducing it in height from to . Introduced in the Jaguar 2.4-litre in 1955, the engine had a stroke of while retaining the bore of to give a capacity of . Despite having a displacement of almost 2.5 litres, the new car was called the "Jaguar 2.4" to create an obvious separation from the old Standard 2½ litre and link it to the now familiar 3.4-litre XK engine. The 2.4s produced were rated at 112 bhp (nett) by the factory, using twin Solex downdraft carburettors. In 1959 the engine was carried over into the new Mark 2, in which it produced SAE gross, still with Solex carburettors. The Jaguar 240 was fitted with an uprated version of the engine, incorporating the straight-port cylinder head and twin SU carburettors delivering 133 bhp SAE gross. The 2.4-litre XK6 was used in the following cars: Jaguar 2.4-litre 'Mark 1' - 1955-59, "B type" cylinder head, unpainted, 2 × Solex B32PB15S carburettors, valve angles 30 degrees inlet, 45 degrees exhaust Jaguar 2.4-litre Mark 2 - 1959-67, "B type" cylinder head, unpainted, 2 × Solex B32PB15S carburettors, valve angles 45 degrees inlet and exhaust Jaguar 240 Mark 2 - 1967-69, "Straight port" cylinder head, unpainted, 2 × SU HD6 carburettors, valve angles 45 degrees inlet and exhaust 3.8-litre The 3.8-litre version was released in 1958, initially for the last of the XK150s and the Mark IX saloon. It retained the 3.4’s bore centres and stroke but was bored out to for a total displacement of (3,781 cc / 230.7 cu-in). The distance between the cylinder bores was sufficiently small that it was decided to fit dry liners to the bores. The 3.8 had a number of detail differences from the 3.4, particularly in its valve gear and carburetion. The standard 3.8 produced SAE gross and up to SAE gross in the XK150SE with the straight port head. The 3.8-litre XK6 was used in the following road cars: Jaguar XK 150 3.8 - 1958-61, "B type" cylinder head, painted dark blue metallic, 2 × SU HD6 carburettors Jaguar XK150 3.8S - 1958-61, "Straight port" cylinder head, painted pumpkin orange, 3 × SU HD8 carburettors Jaguar Mark IX - 1958-61, "B type" cylinder head, painted dark blue metallic, 2 ×