The famed Jaguar XK6 engine was introduced in 1949 and produced until 1994. It was a DOHC inline-6 engine.

3.4

The first use was in the 1949 Jaguar XK120, where it was billed as the 3 1/2 litre. This was a 3.4 L (3449cc) version with a 83mm bore and 96mm stroke and produced 210 hp at its best. It had an iron block and aluminium head. A 4-cylinder XK4 variant was never produced.

In all, the 3.4 litre version was used in the following cars:

Jaguar XK120
Jaguar XK140
Jaguar XK150
Jaguar Mark VII
Jaguar Mark VIII
Jaguar Mark 2
Jaguar 340
Jaguar S-Type (original)
Jaguar C-Type
Jaguar XJ6

3.8

The larger 3.8 L version was released in 1958. It was a bored (to 87mm) version and produced up to 245 hp.

This engine was used in the following cars:

Jaguar XK150
Jaguar Mark 2
Jaguar Mark IX
Jaguar Mark X
Jaguar E-Type
Jaguar S-Type (original)
Jaguar XKSS
Jaguar D-Type

4.2

The 4.2 litre version was officially released in 1965, though racers had been boring the 3.8 out all the way to 4.2 litres for years. The official bore was 93mm, and the engine produced from 240 hp to 265 hp, depending on carburettor or fuel injection.

This engine was used in the following cars:

Jaguar 420
Jaguar 420G
Jaguar E-Type
Jaguar XJ6

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2.4

The 2.4 was an unpopular version of the 1970s. It was a de-stroked (to 76.5mm) version of the 3.4, and produced 133 hp. It was used in the Jaguar Mk1, Jaguar Mk2, and Jaguar 240.