Nov 24

Nov 24 Guide: Jaguar XK SS - a Historical & Technical Appraisal

Jaguar - Jaguar XKSS - Jaguar D-type - 1950s British Cars - 1950s Supercars

Background

After seven years of unprecedented success with the XK120, C-type and D-type, in October 1956 Jaguar announced that it was to officially withdraw from all forms of motor racing.

Having won the Le Mans 24 Hours on four occasions plus a litany of other high profile events, the Coventry firm had nothing left to prove and, as the company’s technical and research departments were overburdened with normal road car development, Jaguar boss Williams Lyons decided the resource-draining works racing programme had to go.

A slimmed down competition department would still develop cars and parts for customers, but in the foreseeable future there would be no factory-entered Jaguars contesting races or rallies.

When the shock decision was made, Jaguar had a good number of D-types in various stages of assembly – everything from bare tubs to nearly complete cars. As the model was still a highly competitive machine at top flight international level, it was still very much in demand - 1956 had most famously seen it win at Le Mans and the Reims 12 Hours. However, to use up most of the remaining tubs, Jaguar conceived a limited run of 25 properly road-equipped D-types dubbed XK SS and planned to dismantle what remained for spare parts.

The inspiration for the XK SS (also referred to as the XK Super Sport) was a D-type owned by ex-factory driver Duncan Hamilton (originally XKC 405, subsequently re-numbered XKC 402). Hamilton’s car had been modified with a taller, full-width windscreen, a pair of windscreen wipers, front quarter windows and a folding canvas roof, but was rather crude compared to Jaguar’s subsequent attempt.

Availability of the XK SS was confirmed in the second week of January 1957 and the first official images were released to the press a couple of weeks later. In addition to comprehensively re-engineered equipment of the type fitted to Duncan Hamilton’s car, the XK SS would also feature a driver and passenger door (as opposed to just the former) and a more comfortable cockpit.

The company stated that, for those customers that wanted to take their XK SS racing, the model had already been homologated as a series production sports car.

Intended primarily for export to the North American market, the XK SS would be one of the fastest, most expensive cars on the market, but the planned-for run of 25 units was soon dramatically scaled back owing to a particularly unfortunate incident.

Browns Lane Factory Fire

On the evening of Tuesday 12th February, a fire broke out in the tyre store at Jaguar’s Browns Lane factory. The fire brigade were quickly on site, but despite their best efforts, the blaze was soon burning uncontrollably. It ripped through the test department, material stores, sawmill and parts of an assembly line where a substantial number of cars were stored.

The fire was eventually brought under control during the early hours of Wednesday 13th.

Despite affecting around one quarter of the Browns Lane complex, William Lyons’ foresight to direct the fire-fighting effort to ensure it did not spread to the main production line, engine assembly area, machine shop and press shop enabled Jaguar to resume production almost immediately.

Even though reconstruction of the damaged plant would not be completed until July, Jaguar went on to have a record year for production in 1957.

Meanwhile, included among the more than 300 cars either destroyed or seriously damaged in the Browns Lane fire were five D-types that had been in various stages of conversion to XK SS trim (chassis XKD543, XKD556, XKD565, XKD571 and XKD574).

By this time, 16 of the anticipated 25 cars had already been completed, but with suddenly much bigger priorities, XK SS production never re-started.

Chassis

The XK SS used a Jaguar D-type central monocoque that was fabricated from 18 gauge magnesium alloy. A tubular aluminium subframe was arc-welded in place to carry the engine and front suspension.

Uniquely, the XK SS did without the D-type’s longitudinal divider between the seats which had facilitated the installation of a rigid metal cover over the passenger side of the cockpit to improve airflow for racing but would have been an inconvenience on what was ostensibly a road car.

Suspension was by double wishbones and torsion bars at the front while at the back Jaguar used a solid axle with trailing links and a transverse torsion bar. Telescopic dampers were fitted all round.

The 12 ¾-inch Dunlop disc brakes as used by the C and D-type were retained. A Plessey servo pump was driven by the propshaft.

Centre locking cast alloy wheels measured 16 x 5.5-inches and were originally shod with Dunlop tyres.

A 37 gallon fuel tank (168-litres) was installed over the rear axle.

Engine / Gearbox

Under the hood was Jaguar’s now legendary dual overhead cam straight six which had originally been designed by William Heynes in 1949.

Like all D-types, the XK SS featured a cast-iron block, a light alloy head, two valves per cylinder, single plug ignition and dry-sump lubrication.

Displacement was the familiar 3442cc thanks to a bore and stroke of 83mm and 106mm respectively.

Fuel feed was via three sidedraught Weber 45 DCO3 carburettors and the compression ratio was 9.0:1.

Despite extra silencing being applied to the left-side exiting dual exhaust, Jaguar still quoted a peak output of 250bhp at 6000rpm and 240lb-ft at 4000rpm.

Transmission was through Jaguar’s own four-speed all-synchromesh gearbox and a Borg & Beck twin-plate clutch. Although a limited-slip diff had been used on some factory race cars since mid-way through 1955, the XK SS got a conventional open differential.

Bodywork

The most significant modification from D-type to XK SS trim concerned the bodywork.

Compared to a regular short-nodse D-type, the XK SS was modified to incorporate a full array of road equipment

At the front, Jaguar fitted quarter bumpers, indicators and glass headlight covers.

Further back, a full height wraparound windscreen was installed along with detachable arced side screens that gave substantially improved airflow protection. The D-type’s distinctive longitudinal cockpit divider was ditched to free up space. Practicality was further enhanced by the addition of a passenger-side door.

Despite the limited production run anticipated, Jaguar also went to the trouble of engineering a proper mohair canvas roof that came supplied with matching cover for when the top was lowered.

Instead of a rear stabilising fin / faired-in head rest, the XK SS came with a luggage rack mounted on the rear deck. This also meant the fuel filler cap (which was normally concealed within said fin) was left exposed on the trimmed rear deck section behind the driver’s seat (and meant fuel could only be added when the roof was lowered).

Further back, tail lights from the XK140 were incorporated to the rear fenders and the opening spare wheel hatch was given an elegant handle and rear licence plate light.

The new full width wraparound bumper was discretely split to enable the original spare wheel hatch to retain its functionality.

Much of this new equipment to include the light bezels, window frames, windscreen wipers, bumpers, luggage rack and trunk lid handle was chrome plated as was the Jaguar XK SS script added to the nose.

Interior

The dash layout was much as in the regular D-type, although the previously exposed Lucas voltage regulator and fuseboard were now concealed, an opening hatch was added to the passenger side and the cavities at either end of the dash were blanked off. The switchgear was also made more user friendly .

Primary instrumentation comprised a large 8000rpm rev counter and 180mph speedometer to the left of the wood-rimmed steering wheel with its three drilled and highly polished alloy spokes. Off to the right were small dials for oil temperature and oil pressure.

While the dash and transmission tunnel were still left-untrimmed, Jaguar fitted seats with a little extra padding and upholstered the sills in black leatherette.

Options

Other than a choice of exterior and interior colours, no official options were offered on the XK SS although Jaguar would most likely have been prepared to carry out the likes of further engine tuning and custom interior appointments should a customer have requested it.

Weight / Performance

The XK SS weighed in at 890kg which represented a 30kg gain over the regular D-type.

Top speed was 150mph and 0-62mph took just 5.2 seconds making the XK SS just about the fastest street car available at the time.

Production Run

Jaguar built 16 examples of the XK SS from D-type tubs during early 1957 with each car given a new XK SS numbered identity.

The five D-types destroyed in the Browns Lane fire had not yet received an XK SS identity.

Because much of the specialised equipment to complete the anticipated 25-car production run was destroyed in the fire, XK SS production did not resume as Jaguar focused on getting normal road car production back up to speed.

In addition to the 16 cars built from unused tubs, Jaguar also converted two additional D-types to XK SS trim during 1958 (chassis XKD 533 and XKD 540).