Jaguar XKSS
Jaguar XKSS

Jaguar XKSS – Transforming the D-Type

When Enzo “II Commendatore” Ferrari said that the Jaguar E-Type was the most beautiful car he ever witnessed, it was hard to say otherwise. However, looking down the line, it becomes obvious that it wasn’t a one-time thing, the Jaguar XKSS sure does rank right up there with the E-Type.

Throughout time, the British brand produced some of the most iconic and eye-pleasing design lines in the automotive industry.

From the Jaguar 100 to the grandparent of top speed, the Jaguar XJ120 and the more recent SVR, automotive enthusiasts have plenty to enjoy.

Jaguar has, however, an intriguing story for one of its crown jewels; a car that wasn’t meant to be, but which is now so hard to find, yet so amazing: The Jaguar XKSS.

Relationship between the D-Type and the Jaguar XKSS

During the mid to late 50s, Jaguar was heavily involved in motorsport, particularly endurance racing.

After winning the famous LeMans 24 hours race twice with the C-Type (1951 and 1953), Jaguar chief engineer and technical director William Heynes pushed aero technology even further and developed the Jaguar D-Type.

1955 Jaguar D Type

front jaguar D Type
1955 Jaguar D-Type 

The tub-like cockpit was aerodynamic and rigid enough to allow Jaguar to win the 24h Le Mans race from 1954 through 1956, battling the likes of Ferrari and Mercedes, each with their own futuristic designs for the time. At the end of 1956, Jaguar took a hard decision to withdraw from motorsport.

Jaguar D-Type Race Car Reproduction

As there were 25 D-type units still laying around in the Browns Lane plant in Coventry, the British manufacturer came with an idea: convert the endurance prototypes to road-legal cars. It was about to become one of the brand’s best takes on a supercar.

Reproduction Jaguar D Type

Reproduction Jaguar
Jaguar D-Type Race Car Reproduction

Jaguar made slight changes to the bodywork of the remaining D-type cars and thus, created the Jaguar XKSS.

The Body of the Jaguar XKSS

The tub-like, or monocoque design was probably Jaguar’s biggest advancement regarding the D-Type and its greatest contribution to the world of racing.

Imported from aircraft models, the XKSS shared the design, featuring aluminium alloy sheets shaped to provide the utmost aerodynamic advantage of the time.

Jaguar XKSS Continuation
Jaguar XKSS Continuation passes the Earl of Wessex (photo: Chris Gage)

Instead of the classic ladder sub-frame, aluminium tubing was used to considerably reduce the weight of the vehicle.  In order to make the XKSS road-legal and bring comfort to the drivers and passengers, slight changes were done to the bodywork.

The stabilizer wing behind the driver was removed. Although its introduction by Malcolm Sayer and the integration of a deformable fuel bag inside were key points that allowed Jaguar to win the 24 hours race, neither of these were particularly useful on the open road.

Other changes include the removal of the divider between the driver and passenger, although a proper passenger seat was never added into the mix.

A passenger-side door was included into the design of the Jaguar XKSS, so no more hopping out of the car, unless desired to.

Jaguar XKSS

With the XKSS version, a fully chrome surrounded windscreen was added as well as side screens on both sides of the car. After all, you were supposed to drive the XKSS without a helmet, and given its speed, the wind would be quite a nuisance.

If by chance you were too caught up driving the XKSS and didn’t notice clouds gathering above, a rudimentary, folding roof was added for protection. Given the capabilities of the car, you could probably race your way home and not get wet, but Jaguar engineers were being thorough.

The XKSS
Jaguar XKSS

In terms of legal compliance, Jaguar had to include chrome front and rear bumpers as well as higher positioned light clusters. Front lights were adorned with chrome borders which would complement the bumpers.

Overall, the car weighs just shy of 2030 lbs. That’s an impressive number by today’s standards, and out-of-this-world during its time.

The good-looking engine – XK6

A sports car engine needs to be powerful. But, as Chief Engineer William Heynes, Walter Hassan and Claude Baily were fire-watching the Coventry factory, they decided it should also look good.

The three engineers aimed to produce engines that were outputting more power than your average unit, thus extending their lifespan without requiring revision, allowing Jaguar to stay ahead of the competition for the years to come.

There were multiple engine iterations coming off the design bench as early as 1943. While the general concept revolved around V-placed cylinders with hemispherical combustion chambers – to allow high brake mean effective pressure – there were several issues that needed be solved before the power units could head to production. Initially, testing was done on 4-cylinder engines.

A variation of 1776cc units, split in XF and XG versions were tested between 1944 and 1953. Issues such as excessive rocker noise and improper flow rates made the engineers to switch to a 6-cylinder architecture in 1951.

Jaguar XK6 EngineThrough 1954, Jaguar increased the cylinder capacity of the XK-6 engine, moving from 1790cc to 1986cc and then to 2483cc by 1955.

In the end, three full-sized aluminium blocks (3.4, 3.8 and 4.2-litre) were selected to undergo production. The Jaguar XKSS was fitted with the 3.4-litre version and triple Webber carburettors, redlining at 5,800rpm and pushing the speedometer to 144mph.

In terms of lubrication, the Jaguar XKSS engine featured a gear-type pump which was later replaced by a Hobourn-Eaton eccentric-lobe unit for increased efficiency. As seen with the initial versions of the D-Type, dangerous vibrations of the 7-bearing heat-treated steel crankshaft were reduced by a Metalastik vibration damper.

It’s hard to know exactly what power output was achieved by the XK6 engine. The iron block and aluminium cylinder head version of the XK6 pushed out 160bhp at 8:1 compression ratio, later boosting to 210bhp and up to 250bhp when switching to a straight port head and 9:1 compression ratio.

Jaguar XKSS used the so-called “wide-angle” cylinder head. Its exhaust valves were positioned 5-degrees more outward the vertical in order to accommodate the larger diameter inlet valves (2” and 2 3/32”).

One of the issues that affected the aluminium cylinder blocks of the XKSS was the gasket failure. As the cylinder liners would sink, they would relax the gasket nip. Fortunately, the issue was fixed by adding securing flanges on the top liners.

Transmission – snuggly gears

Wheelspin? The Jaguar XKSS did not lack it, however, given the lack of a limited slip differential, some tire burning is expected if anything.

The original LeMans gearing would not have been appropriate for the XK SS, as there weren’t really any roads as long and straight as the Mulsanne. Instead, closer-tucked gear ratios were added and, even so, the sharp racing clutch did not go easy on the driver as the car started to roll on the street.

With no flywheel mounted, the throttle would be as sharp as one would expect, engaging the wheels in an instant.

The 4-gear lever in the cockpit hints all too well to the D-type mad racing days. A solid push or pull is required to get into gear, while also matched with a good timing of throttle and clutch. However, once one gets to master the shifting sequence, the feeling is out of this world.

Many would argue the duality of the Jaguar XKSS – not smooth enough for the road and not aggressive enough for the track. As time passed, history proved them wrong and to this day, driving one is a turning point in every car enthusiast’s life.

The Jaguar’s Stopping power

The aerodynamic monocoque wasn’t the only element Jaguar brought over from aviation territory in order to get an edge over its Mercedes and Ferrari rivals.

All-round disc brakes for implemented by Jaguar for the first time, saving countless seconds especially at the end of the Mulsanne straight, where the D-type could brake later than its competitors.

The system translated well into the road-legal XKSS, offering a bold sense of security whenever the brake pedal was pressed.

Road Behaviour of the Jaguar XKSS

Take a racehorse off the track and put it in front of a carriage. Would you expect it to start off slow and maintain a steady pace? Of course not! The same happens with the Jaguar XKSS. While it’s drivable on the road, it breathes racing through all its pores.

Driving the Jaguar XKSS
Jaguar XKSS

There’s plenty of fun to be had with the Jaguar XKSS, but it will be demanding. The engine will pull even from 1500rpm, but the gross of the power is concentrated in the upper third of the rev counter, as with most racecars.

The generator (no alternator was included at the time) required the engine to sit above 2000rpm in order to charge the battery. This would mean keeping the engine revved up and allowing the bulky exhaust to show off its deepest and loudest notes. And while a roaring exhaust is fun, a longer ride would prove to be at least slightly uncomfortable.

Speaking of comfort, the suspension system of the jaguar XKSS was remarkably kind for a racecar. Purists would say that the chassis flexes a bit more compared to D-Type, given the lack of a centre brace in the cockpit.

On the bright side, the windshield did a good job deflecting incoming air currents, is particularly handy on the highway.

Tight corners urged the tail out as the imposed understeering for long straights stability was there to make it happen.

The characteristic bump kickback was also present due to the rack-and-pinion steering, and it only took 2.3 turns to go from lock to lock. Although not assisted, the steering proved to be light, not requiring Popeye’s forearms to make the car turn.

Factory fire in Browns Lane Factory and Rebirth

Jaguar aimed to build 25 units of the XKSS. Unfortunately, a fire took down the Browns Lane factory in Coventry. There was heavy damage done to some of the cars and many engineering plans were lost. Even more, a lot of the tooling and jigs were also burned beyond recovery.

For almost 60 years, that was the whole story of the Jaguar XKSS. The few models that made it out of the factory were sold at huge prices and their value only increased in time.

In 2016, Jaguar came out to fulfil its promise from 60 years ago. With over 10,000 man-hours, the company set out to build the remaining XKSS units up to the 25-piece mark.

This wasn’t just restoration or a replica. The “new” Jaguar XKSS was a perfect match, down to the last rivet position and cam tuning.

reproduction Jaguar XKSS
Jaguar XKSS

All recovered engineering drawings and plans were carefully examined and used to accurately spec the modern, yet old XKSS units. However, since most of the plans for the XK-6 engine were lost, the engineers had to literally scut an existing engine in half in order to reverse-engineer it.

interior on Jaguar XKSS

Delivery of the Jaguar XKSS models started in early 2017, and the units were instantly acquired by a select group of brand’s customers and collectors.

Each car was sold for roughly $1.3 million. Given how rare the model is and the factory-quality of the build, it is easy to call it a bargain.

Conclusion

Pay homage to one of the greatest endurance cars that ever existed, the XKSS came to life from the scraps of its predecessor.

What started out as an attempt to benefit from the emerging sportscar market in US and Europe turned out to be one of the earliest pure-exotic cars.

Long before the likes of Ferrari and Lamborghini brought out their high-performance units to the city roads, Jaguar took the authentic LeMans racer, stripped the minimum necessary, added even fewer tamed parts, and delivered the XKSS – a design so good and adored that it made the British brand restart production six decades later.