The Jaguar XJ220 Prototype

Engine

At the heart of the XJ220 prototype lay a highly developed version of Jaguar’s production V12 engine. Bored and stroked from 90x70mm to 92x78mm, the swept volume was increased 16% to 6,222cc and ran a compression ration of 10 to 1. Its all alloy block was machined down to save space and weight, and a magnesium sump cover plate on the bottom provided dry-sump lubrication to allow the engine to sit low down in the chassis.

Valve gear

On top of each bank of cylinders was a twin-cam, four-valve per cylinder alloy head. The magnesium rocker covers had ‘Jaguar V12 four-valve’ picked out in polished relief, and in the vee between the heads the intake ports lead into 12 vertical velocity stacks. In place of a distributor, the V12 used individual coils mounted on each spark plug cap. Both the ignition and the sequential fuel injection used Zytek microprocessor control.

Cooling

Preventing 500+ bhp of mid-mounted V12 overheating, IMI Marston came up with an alloy radiator package that also contained heat exchangers for the engine and transmission oil. Front-mounted and assisted by electric fans, cooling air was drawn in from a duct under the nose of the car.

Power delivery

400+ ft lb of torque was transmitted through a 7.25-in twin-plate AP Racing clutch sitting behind a much smaller flywheel. With a smaller diameter ring gear, the V12 used a starter motor mounted towards the front of the block, driving through a two-piece universally jointed quill shaft.

Bolted to the back of the block, a special casting housed the rear bevel differential with a viscous coupling across the outputs to progressively direct more torque to the wheel with the most grip. A shaft from the clutch passed under this, taking the drive to a five-speed gearbox bolted behind.

To fit in with the car’s rearward weight bias, the torque was split 31% to the front and 69% to the rear. Drive to the front passed along a quill shaft where the distributor shaft would ordinarily have been, located with a central bearing and a casting bolted to the front of the block.

The front differential was a conventional bevel gear type with another viscous coupling across it but, because the drive to it spins slightly slower than the output to the rear differential, it needed a 2.76:1 ratio rather than the rear’s 2.88:1 to turn the wheels at the same speed.

Suspension

No suspension loads pass directly into the chassis. At the rear, double unequal-length wishbones were pivoted directly on the transaxle casings at the bottom, and via a small subframe to the same casings at the top. Two Koni spring/damper units per side were mounted almost horizontally, and operated by a bell-crank that was part of the upper wishbone. Cast alloy uprights pivoted on bearings to allow for a four-wheel-steering system to be installed later.

The suspension layout at the front was similar, effectively unequal length double wishbones, but with a welded steel subframe holding the front differential, upper and lower wishbones and the steering rack. A single lay-down Koni spring/damper unit was used each side, operated from the lower wishbone via a pushrod and rocker.

Brakes

To stop the XJ220 from 200+ mph, AP racing 13-in diameter ventilated discs and four-pot calipers with differential piston sizes were used on each wheel. An electrically driven Wabco hydraulic power booster was fitted to bring pedal pressures down. Similarly, Wabco also supplied the four-channel anti-lock brake system.

Chassis

To tie everything together, a fully bonded alloy chassis was used. Using high manganese aluminium alloy sheets and single part epoxy glue to join the panels together, provided a very stiff, lightweight structure with excellent corrosion resistance that is very strong and deforms progressively under impact.

Using only flat or folded sheets of aluminium meant that there was no tooling expense to produce pressings, and the components could also be produced relatively quickly. The finished chassis tub weighed less than 350 lb.

Cutaway drawing of the original XJ220 prototype