“As the proud owner of a 1990 XJ-S V12 convertible called ‘Ruby’, I regularly attend classic car shows. There’s always plenty of interest in ‘Ruby’, but many visitors are largely unaware of the history of this model, so I’ve penned this brief article for those who want to know more about this beautiful car and the legendary V12 engine.”
Stephen Lewis. Owner of ‘Ruby’.
Introduced on the 10th September 1975, the design and development of the XJ-S began in the late 1960s under the code name “Project XJ27”. Initially penned by Malcolm Sayer, the design was completed by the Jaguar in-house design team, headed by Doug Thorpe, after Malcolm Sayer’s death in 1970.
Contrary to popular belief the XJ-S was never intended to be an ‘E’-Type replacement. The ‘E’-Type was originally designed as a raw, seat-of-the-pants, out-and-out sports car, but continuous modifications (mainly to suit the USA market) had made it soft, bloated and unattractive.
The XJ-S was conceived as a grand tourer (GT); able to cover long distances at high speed with the minimum of fuss and in the maximum of comfort, it was designed from the start to take advantage of Jaguar’s legendary V12 engine.
Jaguar launched the XJ-S in the middle of a fuel crisis, when the market for a 5.3-litre V12 grand tourer was small. Car enthusiasts, hoping for an ‘E’-Type replacement, were disappointed with the design, the buttresses behind the windows garnering particular criticism. Contrary to popular myth, these had nothing to do with the idea of a mid-engine layout being considered during development, but are an intrinsic part of the aerodynamics, key to the idea that how you leave the air flow is just as important as to how you enter it. The XJ-S was initially available with a choice of a manual or an automatic transmission, with the 0-60 mph time being 7.6 seconds (automatic models) and the top speed 140 mph.
In July 1981, the XJ-S received the new High-Efficiency (HE) V12 engine, which not only improved fuel consumption, but produced more power and torque. At the same time the XJ-S was treated to a minor facelift (see image at right), gaining higher gearing (a 2.88 diff ratio against 3.07), a move from six-inch to 6.5×15 five-spoke (starfish) alloy wheels with 215/70 tyres, revised suspension and steering, body-coloured boot trim, and the stark interior, which was so modern at the original launch, was given a more traditional wood and leather makeover, with burled elm inserts on dashboard and doors.
In 1983 Jaguar introduced the XJ-SC, which was initially available with new the AJ6, 3.6-litre straight six engine and a manual gearbox. The XJ-SC model, developed in response to demand from US dealers for an open car, was not a full convertible, but rather a cabriolet, with a non-removable centre targa-type structure, fixed cant rails above the doors, and fixed rear quarter windows. The coupé's rear seats were removed in order to make space for the removable soft top, making it a 2-seat car.
The XJ-SC Cabriolet.
The cabriolet would prove to be short-lived, as Jaguar had enlisted the help of Karmann to produce a full convertible XJ-S, which was launched in 1988. Without the flying buttresses the styling was transformed, and the car immediately looked more modern.
In 1991, the XJ-S was given a major facelift by the new owners, Ford. Costing £50 million, the facelift involved significant bodyshell changes, with some 180 individual panels being either new or revised. The boot lid was shortened, the sills flared out at the trailing edge and the windscreen was a flush-fitting bonded-in item. The bonnet panel was also standardised across the range, with the V12 cars sharing the bulged panel previously used for the six-cylinder cars. Meanwhile, the inside now featured many XJ40 saloon parts, and the old vertical instruments were replaced by conventional analogue dials. The model’s signature buttresses appeared smaller due to changes to the rear window trim, despite having identical glass apertures. Ford also dropped the hyphen from the model’s name, marketing it as the XJS. A similarly revised convertible arrived in 1992, featuring a revised rear pan structure which allowed small rear seats to be included.
In May 1993, the V12 engine capacity was increased to 6.0 litres and mated to a GM 4L80-E four-speed automatic gearbox, with a lock-up overdrive top gear and switchable Sport mode. From June 1994 the AJ6 engine in the straight-six engined car was replaced with the much-improved AJ16.
To coincide with its 20th birthday, the ‘Celebration’ model arrived in 1995, featuring diamond-turned alloy wheels, embossed seats and a wood-rimmed steering wheel. After 21 years in production and 73,207 cars produced, the XJS was finally discontinued in 1996, and despite what you may read about the XJS’s apparent lack of success in the market, its production figures were far in excess of what the ‘E’-Type had achieved, and it is still Jaguar’s most successful sports car.
The final version of the XJS.
The Jaguar V12 Engine - An Iron Fist in a Velvet Glove.
The 5.3 litre V12, with fuel injection.
In 1951, and with the XK engine in production, Jaguar’s engineering department commenced a development programme for the next generation of power units. The design team investigated various configurations, including a V6 and a V8, but neither of these were refined enough for Jaguar, and the V12 configuration was selected.
The logical approach was to take two XK engines, mount them in a 60° ‘V’ on a common crankcase and share a single crankshaft. Work started on such an engine, but it soon became apparent that one of the drawbacks was the double overhead camshaft (DOHC) arrangement, which made the engine very wide. It was at this point, with Jaguar’s production and sales increasing, that the team had to turn to other more pressing issues and the V12 programme was put to one side.
In 1963 the design team returned to the V12 engine development, but the four-cam arrangement was too heavy, large, complex, and costly for production. In addition it would not have fitted the car for which it was intended, the XJ saloon, or the car in which it was to debut; the ‘E’-Type. Jaguar intended to launch the XJ saloon, then in development, with the V12 engine in 1968, so the pressure was on to make an efficient, road-going, thoroughbred unit. The cam chain drive, the cylinder head layout, the combustion chamber shape, the bore and stroke, and the change to one camshaft per bank, plus numerous other details, were all re-visited over the next few years. Jaguar also pioneered the use of light aluminium alloys for the cylinder block, cylinder heads and pistons, which reduced the overall weight of the engine. Jaguar wanted to make use of fuel injection for the V12 but there wasn’t a working British system available at the time, so Jaguar decided to install four Zenith-Stromberg 175 CDSE carburettors.
However, the engine was not ready in time to power the XJ saloon at its launch in September 1968, so the existing series 2 E-Type 2+2 was modified to accept it, and the new engine was introduced to the public on the 29th March 1971. Although Ferrari, Lamborghini and others had produced V12 engines, these were hand-built in small quantities, and much was made of the world’s first quantity production V12 engine.
And what an engine it was ! The 5.3 litre (5,344 cc) production engine had an oversquare 90 mm bore x 70 mm stroke, producing up to 295 bhp and 295 Ibft of torque, depending on emission controls and compression ratio. But the attribute constantly quoted by the press was its refinement; it was smooth, quiet, and unstressed, and gave the XJ saloon, introduced less than a year later, performance to match the top sports cars of the day.
Despite being acclaimed for its refinement and performance, the XJ12 saloon came in for some heavy criticism for its thirst, with one test quoting 11.4 mpg. In 1973 the carburettors were replaced by a Bosch D-Jetronic fuel-injection system, and although overall engine efficiency was improved, fuel consumption was not. In 1981 Jaguar revised the engine, introducing the ‘high efficiency’, or HE, unit, which saw the cylinder head and pistons replaced with a new design from Swiss engineer Michael May. May’s design gave the engine an unusually high compression ratio with a relatively lean fuel mixture, and although power levels remained similar to the previous model, fuel economy was improved by some 50 per cent, taking the average to 22 mpg.
The V12 always had huge potential for further development, and the design team considered many revisions, including taking the stroke to 84 mm, but the costs proved too high. A 6.4 litre version was built and tested, but it wasn’t until 1993 that the V12’s capacity was increased to 5,994 cc. The new 6.0 litre unit continued to power models in the range into the 1990’s, becoming one of the best automotive engines to have ever been produced anywhere. Jaguar made a total of 161,583 V12-engined cars.
The 6.0 litre V12.
“Driving a Jaguar V 12-engined car is like nothing you’ve ever experienced before on the road. Plant your foot to the Woolton-carpeted floor and the acceleration is phenomenal and all the more astonishing because, other than the subdued but throaty exhaust tone, there’s isn’t any indication that the engine is working. It’s silky-smooth, composed, imperturbable, and unruffled. It just goes, and before you know it 100mph is reached. It’s how I’d imagine a magic carpet ride to be.”