Jaguar V12 engine

An evolution of the 1964 DOHC prototype “XJ13” engine, the Jaguar V12 engine is a family of SOHC internal combustion V12 engines with a common block design, that were mass-produced by Jaguar Cars for a quarter of a century, from 1971 to 1997, mostly as 5.3‑litres, but later also as 6‑litres, and 7‑litre versions that were deployed in racing. At launch, the engine was the only V12 in mass-production. For 17 years, Jaguar was the only company in the world consistently producing luxury four-door saloons with a V12 engine. The V12 powered all three series of the original Jaguar XJ luxury saloons, as well as its second generation XJ40 and X305 successors.

Originally fitted with carburettors, the SOHC V12s received electronic fuel injection in 1975. In 1981, the engines were improved with higher efficiency (HE) cylinder heads. Including the V12 E-Type mark 3 models, and in the XJS (from 1975 to 1996), Jaguar made a total of 161,583 SOHC V12-engined cars. The Jaguar V12 was regarded as one of the premier power plants of the 1970s and 1980s. After launching the second generation XJ series in 1986, Jaguar developed their V12 into the racing engines that brought two overall victories at the 24 hours of Le Mans endurance races of 1988 and 1990.

Remarkably, three decades earlier, the engine was initiated in 1951 by Claude Baily as a prototype design for an intended Le Mans racecar: the Jaguar XJ13 - as well as for planned use in Jaguar’s range of luxury and sports cars. After building six DOHC engines, three of which were extensively tested in cars, the XJ13 project was terminated in 1967, before the car ever entered into competition. Under the direction of Jaguar Chief Engineer William Heynes, the DOHC V12 engine design was reworked by engineers Walter Hassan and Harry Mundy into a road-going SOHC production-vehicle version, first installed in the Jaguar E-Type mark 3 of 1971. The SOHC V12 was just the second production engine design in Jaguar's history, after the 1949 straight-six XK engine, built through 1992. It uses an all-aluminium block and cylinder heads with removable wet steel liners, and single overhead camshafts with two valves per cylinder.

Initial designs for a V12 engine were produced by engineer Claude Bailey as early as 1951, with a view to using it in a Le Mans race-car. Bailey's original 8.0 L design used double overhead camshafts heads sharing the same basic layout as the inline 6-cylinder XK engine, in order to allow for a relatively high redline. Even after Jaguar withdrew from racing in 1957, the V12 design continued to be refined, and Bailey proposed a range of displacements from 7.6 L (sharing 87 mm bore and 106 mm stroke measurements with the 3.8 L XK) down to 5.0 L (sharing the 2.4 L XK's 83 mm bore and 76.5 mm stroke). In 1962 Bailey was instructed to begin prototype tooling and bench testing of a 5.0 L design, having settled on an 87 mm bore and 70 mm stroke.

By 1964 several incarnations of the V12 engine were being tested, including versions meant for racing and others for installation into production cars. An all-aluminium quad-cam design with fuel injection was created for the XJ13, while cast iron blocks and heads, and other double and single overhead cam head designs were created for use in a production road car version. These production versions of the engine were tested in Mark X saloons.

After the XJ13 project was cancelled the team of Hassan and Mundy designed a new single overhead cam head, with the camshaft lobes acting directly on vertically-inclined valves through bucket tappets. This was similar to the cylinder head design of the contemporary Rover 2000, with which the Jaguar V12 also shared the use of dished 'Heron' pistons. These changes reduced complexity, weight, size and noise, and were anticipated to help the engine meet future emissions standards.

The revised head design by Hassan and Mundy also had longer, more restrictive inlet ports sacrificing top-end power but which—along with an increase in displacement to 5.3 litres (5,344 cc) (90 mm bore x 70 mm stroke)—greatly improved performance at lower and mid-range engine speeds, which was more desirable in heavier luxury cars. The chain-driven SOHC heads and the softer valve springs fitted to reduce valve train noise resulted in the red line being lowered to 6,500 rpm from the 8,000 rpm of the original DOHC design.

The engine was continuously refined with various carburettor and fuel injection arrangements before finally seeing production in the Series III E-Type in 1971. At the time, it was the only V12 engine being mass-produced and it was the first such engine since the Lincoln Zephyr V12 of 1936-1948.