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Jaguar Speed

A look at the Jaguar XJ-SC ragtop -resplendent with its big V12 engine.

Words by Michael Knowling, Pix by Julian Edgar

Click on pics to view larger images


This article was first published in 2004.

One of the most unsung of exotic sports cars must surely be the Jaguar XJ-SC V12. A sweet V12 engine, good aerodynamics, a 230+ km/h top-end and Jaguar prestige combine to create a package that we reckon deserves more attention.

Time for a quick background check.

The Jaguar XJ-S hardtop coupe debuted in 1975 as the successor to the famous E-Type. The new XJ-S was a relatively large vehicle with more focus on space and practicality and was pitched squarely at the lucrative American market. At the time of release, however, the XJ-S was much maligned by the media – especially for its dubious build quality in the early years.

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Running changes were made to improve various aspects of the XJ-S, but the biggest change came in the early ‘80s in the wake of the OPEC fuel crisis. In 1980, Jaguar enlisted the services of engineering guru Michael May (who was widely recognised for his previous work with Porsche). Michael headed a team that sought to improve the existing 5.3-litre V12’s poor fuel consumption. This involved redesigning the heads (with particular improvements in combustion swirl) and lifting the compression ratio to a massive 12.5:1. (Leaded fuel had a very high octane rating back then!) It was 1982 when these revised V12s – dubbed HE (High Efficiency) – were released onto the market.

In 1984/1985, Jaguar then expanded the XJ-S range with a cabriolet version. This unusual machine features two lift-off solid roof panels and the option of a folding rear hood or fixed rear window. This was the first open-top Jag since the E-Type Roadster, which died in 1974. Interestingly, safety regulations limited the cabriolet to a seating capacity of just two – pretty abysmal considering the overall size of the car! Not surprisingly, the cabriolet model was axed during 1988 when it was replaced by the ‘proper’ convertible.

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The XJ-SC convertible was first previewed at the 1988 Geneva motorshow, where it attracted plenty of attention. It was the vehicle to challenge the existing Mercedes-Benz SL and Porsche 911. Like the discontinued cabriolet, the XJ convertible was based on the same underpinnings as the XJ-S but structural stiffening was added to the A-pillars, sills, underfloor and bulkhead. This gave more torsional stiffness than the cabriolet. The frameless doors that were introduced were also extensively tested for strength and durability.

The XJ-SC convertible’s soft-top hood is manually released by twin latches on the windscreen header rail but it has an automated retraction mechanism activated by a switch in the console.  The hood motor and hydraulic pump are hidden in one side of the storage compartment. Interestingly, the rear window is made of glass and comes with an electric demister – no cheap, plastic-type rear window here!

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Under the skin, the suspension remained largely the same as the XJ-S. That means the front uses double wishbones, coil springs and an anti-roll bar. The rear suspension is fully independent with lower transverse wishbones and driveshafts acting as upper links. Drive is to the rear wheels via a limited slip centre differential.

A four-wheel-disc brake system came standard along with ABS control incorporating a new yaw sensor. The rack-and-pinion steering came power assisted.

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Many of the XJ-SC’s body parts are interchangeable with the XJ-S coupe, but no less than one-third of the pressings were new or modified. There were lots of subtle changes, such as the adoption of one-piece door windows to reduce weight and aid aerodynamics. Still, total weight of the XJ-SC was about 100kg up on the XJ-S – the ragtop (with its added chassis stiffening and mechanical roof mechanism) weighed a substantial 1900kg. The XJ convertible also has an aerodynamic 0.39Cd versus the hardtop coupe’s 0.38Cd.

Standard interior features of this fully-optioned cat includes an adjustable reach steering column, cruise control, central locking, electric windows, electric aerial, trip computer, air conditioning, heated front seats with electric lumbar adjust and a leather/walnut veneer trim. It’s a very comfortable place to be – as you’d expect.

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Introduced to Australia in March 1988, the XJ-SC was one of the fastest and most refined open-top cars in the world. Under the bonnet was the 60-degree 5.3-litre V12 derived from the E-Type. Using a 90mm bore and 70mm stroke, the SOHC, 2-valve-per-cylinder engine (in HE-spec) uses a 12.5:1 compression ratio and Lucas-enhanced electronic fuel injection. The engine features all-alloy construction in an attempt to minimise weight. Depending on market, max power is 217kW at 5500 rpm. The Australian version – with a low 11.5:1 compression ratio for unleaded fuel and cat-type exhaust – made just 195kW at 5250 rpm with up to 377Nm of torque.

Equipped with the standard 3-speed auto (which we believe is a GM Turbo 400) the 217kW-spec XJ-SC 5.3-litre V12 is claimed to accelerate from standstill to 60 mph (96 km/h) in 7.9-seconds. Top speed is of this model is also 241 km/h - almost 2 km/h slower than claimed for the coupe stablemate. The 195kW Australian version, on the other hand, accelerates to 100 km/h in the low 9s and peaks at a shade over 230 km/h.

And then – just when you thought this was one quick convertible – along came more power!

In late 1993, the faithful 5.3-litre V12 was stroked to a massive 6.0-litres using a 78.5mm throw crankshaft. Amongst several other engineering changes, the stroked V12 was now good for 234kW at 5400 rpm together with 463Nm of torque at 3650 rpm. (Note that this engine was also shared with the XJ-S coupe and XJ-12). A 4-speed auto was fitted as standard to the 6.0-litre convertible. Not surprisingly, the 6.0-litre XJ-SC can accelerate to 100 km/h in the mid 7s and run to around 250 km/h. Impressive stuff!

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In Australia, the original 5.3-litre XJ-SC was updated with a 4-speed auto in 1993 but was discontinued during 1994. With the big 6.0-litre V12 having established itself as the gun performer of the range, a more affordable 4.0-litre straight-six XJ-SC was phased in during 1992. Sales were not strong, however, so the 6.0-litre XJ-SC was axed in 1995 and the 4.0-litre model lived only until the next year. The entire XJ-S series was replaced in 1996.

A Lightly Tweaked Example...

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The XJ-SC seen in these pics was recently purchased by David Lawrie of Kingston, South Australia. David tells us, “I’ve always enjoyed motorbikes and cars and, after I sold my Harley Davidson, my wife suggested we buy a convertible – something big enough that the two of us and our three kids could enjoy.”

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Although its history is a little sketchy, this car has recently been treated to a minor body restoration including a new coat of gunmetal grey paint. The marque’s linearity can also be seen in the E-Type style bonnet vents that have been added. US-spec dual-lens headlights, fog-lights and a rear spoiler were also fitted. All work was done by the previous owner.

Under the bonnet there’s the big 6.0-litre V12 engine. Power has been lifted with the change to a twin 2 ¼-inch stainless system and MoTEC management system. A Crane Fireball ignition booster is also installed. Interestingly, one of those damn-near unbreakable Supra 5-speed gearboxes has also been fitted behind the V12 – rest assured there’s always plenty of torque on tap to pull any gear!

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We had a chance to drive the vehicle and can vouch that it’s a very refined, sweet vehicle with ample on-demand performance. The sound of those twelve cylinders firing is also pretty rousing when you’ve got the roof down!

Suspension-wise, the car has been brought down a few inches and has received the usual bush and shock-related maintenance work. The guards are capably filled by PCW polished 5-spoke 18s wearing 245 and 255 width front and rear Kumhos.

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Inside, the previous owner opted to rejuvenate the standard leather trim and has installed an up-to-date Alpine CD/tuner sound system. A small diameter sports steering wheel adds to the agile feel of this big cat.

David enthuses, “We’ve owned the car for only a couple of months but already the whole family loves it. It’s very smooth and great to drive – in fact, my wife loves to take it out and take the kids for a run along the coast.”

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Sounds like this cat has found a loving new family. Maybe we should all look into adopting a pre-loved cat.

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