Jaguar V12 engine

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Jaguar V12 engine
File:Jaguar 5.3 V12 Engine.jpg
Jaguar 5.3 V12 engine in an XJS (1992)
ManufacturerJaguar Cars
Production1971–1996
SuccessorJaguar AJ-V8

Jaguar's V12 piston engine was one of the premiere powerplants of the 1970s and 1980s. It was first seen in the Series 3 E-type of 1971 and was based loosely on an earlier design intended for a Le Mans car, the ill-fated Jaguar XJ13. The V12 was only Jaguar's second engine design to go into production in the history of the company. The all-alloy block was fitted with removable wet liners and had a SOHC 2-valve alloy head with flat combustion chambers.

Development

Initial designs for the V12 were produced as early as 1954, with a view to using it in a Le Mans car. The engine was to be a 4.4 litre, quad-cam engine with a high redline. After Jaguar withdrew from racing, the V12 designs lay forgotten until the early 1960s when they were re-examined as a possible powerplant for a limousine which ultimately never reached production. In developing the engine for road use the gear-driven quad-cam configuration was judged to be too complex and heavy, as well as unacceptably noisy for a luxury car. The cylinder heads were replaced with more conventional 2-valve SOHC designs, reducing complexity, weight and noise. The revised head design had restrictive inlet ports which sacrificed top-end power but which, along with an increase in displacement to 5.3 litres, greatly improved performance at low-mid engine speeds, which was desirable in what was planned to be a heavy luxury car. The SOHC heads and the soft valve springs fitted to reduce valvetrain noise resulted in the redline being lowered to 6000rpm from the 8000 of the original quad-cam design. When the limousine project was cancelled the engine was again left for a number of years before finally seeing production in the series III E-type in 1971.

5.3

The 5.3 L (5343 cc) version had an oversquare 90 mm bore and 70 mm stroke. It produced 210 kW (285 hp) (245 to 299 bhp (223 kW) depending on emission controls and compression ratio) and 400 Nm (295 ft·lbf) in fuel-injected form. Right from the start of production in 1971 for the Series 3 E-Type, the V12 engine had Lucas OPUS electronic ignition. This system was used until 1982 when the Lucas CEI system was introduced. Initially the OPUS ignition amplifier unit was secured directly to the engine between the cylinder heads and had problems due to overheating. Later cars had the ignition amplifier moved away from the engine where it could get air flow for cooling. Originally the V12 was supposed to get an advanced Fuel Injection system under development by AE Brico but this plan was cancelled at a late stage, possibly due to concerns that the design was too similar to Bosch products. The V12 as used in the Series 3 E-Types and the S1 XJ12 cars had four Zenith-Stromberg side draft carburetors. After April 1975, the V12 engine used in the S2 XJ12 and the new XJ-S had a Lucas fuel injection system which was based around the Bosch D-Jetronic system.

This version was used in the following cars:

5.3 HE

A High-Efficiency 5.3 HE version debuted in 1981. This used the special high-swirl design 'May' cylinder heads, and had an unusually high compression ratio (10.5:1 - 12.5:1 depending on market and year). In any given market, power levels remained similar to the previous model, but fuel economy was improved by nearly 50%. The HE V12 engines had a fuel injection or engine control system from Lucas which was based on the Bosch P-Jetronic system.

The Lucas CEI ignition system continued until mid 1989, when it was superseded on the XJ-S by a system from Magneti Marelli. Series 3 XJ12 and Daimler Double Six cars used the Lucas CEI system until the end of production in 1992. The Marelli ignition system was used until the end of XJ-S production and on the 6.0L V12 used in the XJ81 four door saloons made in 1993-1994.

The 6.0 litre X305 1995-96 XJ12 and Daimler Double-Six cars had a new Nippondenso distributor-less crank-fired ignition system with coil packs very similar to Ford EDIS-6 units. This engine cannot be tuned up to the extant that previous versions were due to poorer gas flow. Another problem with the use of the 'May' head design is that the chamber design creates a number of 'hot spots' under certain operating conditions that can cause runaway detonation and consequent engine failure. This was more of a problem with the 5.3L version than the later 6.0L derivative and affected a small number of vehicles in markets where sustained high-speed driving (well over 120mph) was followed by a period of closed-throttle running. This failure mode was generally only seen in Germany where such conditions could be created on the Autobahn.

The 5.3 HE was used in these cars:

6.0 HE

The engine was stroked to 78.5 mm in 1992 for a displacement of 6.0 L (5994 cc) to make this the most powerful Jaguar production engine to date. The last Jaguar V12 engine was produced on April 17, 1997.

The 6.0 HE was used in the following cars:

TWR/Lister

In 1985, Tom Walkinshaw Racing became Jaguar's official team in World Endurance Championship, taking over the project from American team Group 44. Their first car, XJR6, used the 6.0 L engine, but in the following year the engine was upgraded to 6.9 L and in 1988 the XJR9 used the engine's most famous displacement of 7.0 L. By 1991, the V12 was good for 7.4 L inside the XJR12, developing an impressive 750 bhp (559 kW)

TWR also upgraded production Jaguar cars (usually XJ-Ss), with a variety of styling, handling and performance modifications. Most of the cars thus modified were straight from the Jaguar factory and sold through Jaguar dealerships. By 1989, TWR were selling moderate numbers of XJ-Ss fitted with a 6.0 litre version of the V12, which pre-dated the Jaguar production version by some 3 years.

Lister Cars, a well-known Jaguar tuner with a long history of technical collaboration with the British automaker, was the first to use the TWR-tuned engine in a road car. In 1991, they fitted the 7.0 L (6996 cc/427 in³) version of the engine, with a 94 mm (3.7 in) bore and 84 mm (3.3 in) stroke, into a modified Jaguar XJS, which was rebadged Lister Le Mans. This engine officially produced 407.2 kW (546 hp) and 786.37 N·m (580 ft·lbf). From 1993, Lister owner Laurence Pearce produced the company's first design the Lister Storm, which, naturally, continued using the V12 engine, both on the road and on the track, the car becoming a mainstay of the FIA GT Championship and several national championships for the following decade.

See also