The Shape

The XJ13's shape had been evolved by Malcolm Sayer -the aerodynamicist responsible for the C-type, D-type, E-type and XJS - for maximum speed on the Mulsanne Straight and with its oval grill and large haunches over the wheels. The XJ13, the car's code-named, clearly bore a strong resemblance to the D-type.


Suspension

The suspension front and rear design was in principle adapted from the E-type, except that the visually similar front suspension wishbone forgings were sprung by coil springs not torsion bars. The rear suspension used the driveshaft each side as the top member, again similar to the E-type. A lower wishbone and trailing arm located the hub. Unlike the E-type only one coil spring and damper was used on each side and the brakes were mounted outboard.


Structure

The construction was similar to those on the earlier D-type: aluminium panels riveted together to form a monocoque. For XJ13 however, the body was divided into three sections, termed body front structure, body centre structure, and body rear structure. The front and centre structures combined to form the very strong monocoque which carried the driver, who sat between two deep sills. These sills contained two of the car’s three bag-tanks for fuel, the third mounted across the car behind the driver.

The placement of the fuel tanks was more important than might be supposed, as one issue with the D-type had been the change in front/rear weight ratio as its rear-mounted tank had emptied, markedly affecting handling and braking bias. Splitting the capacity and placing tanks in the sills minimised this tendency on XJ13.

The third element, the rear body structure, consisted of unstressed rear outer body panels which contained the spare wheel compartment. The rear body covered the engine which was anchored to the centre section’s rear bulkhead and was itself a stressed members as it carried the ZF five speed synchromesh transaxle and the rear suspension.


The Engine

The power unit was a dry-sumped 4,994cc V12 featuring XK aluminium cylinder heads, each carrying two camshafts. The cylinder block was also aluminium, with cast iron dry liners, Brico pistons and Dykes rings.The pistons were carried by forged, polished connecting rods and the seven-bearing crankshaft was in nitrided En40 steel. The compression ratio was typically 10:1 and the mixture was supplied by Lucas mechanical fuel injection.

Although an impressive looking unit, its power output was initially a disappointing 430bhp. Development of the engine eventually saw power improve to 502bhp at 7,600rpm with 386 lb ft torque at 6,300rpm.


Testing and Development

XJ13 was running by March 1966, though no racing programme was instigated. Even testing of the car had been banned by Sir William Lyons. This wasn’t to stop those closely concerned with the development of XJ13, who secretly transported the car to the MIRA test ground where test development driver Norman Dewis took it around MIRA’s banked circuit at gradually increasing speeds. Norman found the car to be somewhat raw, with “terrible” handling. Given that this was Jaguar’s first mid-engined car there was bound to be a learning process.

Development of XJ13 was much assisted by data gathered from sampling the opposition when, in March 1966, Norman Dewis borrowed a GT40 from Ford. Though this car was a 4.7-litre road version, analysis of its steering and suspension proved very useful.

Eventually lap times at MIRA had improved to 160mph, with the fastest lap being by David Hobbs on 9th July 1967 at 161.6mph


Retirement

After the summer of 1967, XJ13 was retired without ever returning to Le Mans. In reality it was unlikely that there would ever have been a return, but the imposition of a 3.0 litre limit on sports prototypes for the 1968 Le Mans guaranteed it.

In 1971, with the launch of the Series 3 E-type, XJ13 was taken out of storage to be filmed at MIRA for a publicity video. Internal corrosion in XJ13’s magnesium wheels caused one of them to disintegrate at speed rolling the car and nearly destroying it. Some years later, the car was rebuilt to a specification similar to the original, using body jigs from its original construction.