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VINTAGE: Jaguar GTP Designed for LeMans
Written by: Wouter Melissen
UltimateCarPage.com   http://www.ultimatecarpage.com
06/26/2009
Le Mans (FR)
 
With five victories in seven years, Jaguar's dominance in the 24 Hours of Le Mans race was total. After the last victory, in 1957, the rules were changed, leaving Jaguar's D-Type obsolete. This effectively ended Jaguar's interest in sportscar racing.

Chassis 006 was built new for the 1984 season, specifically for long-distance events. Part of the two-car Le Mans team,it was forced to retire after an accident. The car is shown during a support race of the 2008 Le Mans. (Photo: Wouter Melissen) » More Photos
Halfway through the 1960s, work was started on a completely new V-12-powered sports car, to challenge Ferrari and Ford at Le Mans. One XJ 13, as it was called, was completed and tested, but the project was dropped for unclear reasons.

After Jaguar's withdrawal, it was up to privateers to defend the honors of the leaping cat. One of the premier Jaguar privateers was Bob Tullius, whose Group 44 racing first campaigned a Jaguar in 1974. He won the Sports Car Club of America’s B production category with a mildly modified V-12 E-Type. Over the years, he kept competing with V-12 Jaguars in the SCCA championships and in Trans Am. When the new IMSA GTP class was formed, Tullius constructed a prototype racer around the V-12 he knew so well.

Built in 1984, chassis 007 was raced for the best part of two seasons. It is seen here at the 2009 Amelia Island Concours d'Elegance, where Group 44's rich racing career was celebrated. (Photo: Wouter Melissen) » More Photos
At Le Mans, there was a class for IMSA GTP cars, so this could end up as Jaguar's return to the French track. That foresight sparked interested in Coventry and with factory backing, work was started in the Winchester, Virginia, headquarters of Group 44 racing early in 1981. The prototype would be aptly dubbed XJR-5; Group 44's previous four cars were XJR 1 - 4.

Hired as designer was Lee Dykstra, whose Special Chassis Inc. had designed a successful ground-effects racer in 1980. Dykstra decided to use the long and relatively heavy V-12 engine as stressed chassis member. The engine was bolted directly on the aluminum monocoque, supported by four stiffening struts bolted on the firewall. The slim design was completed by attaching the rear suspension on the transaxle,
leaving plenty of space for underbody aerodynamics.

Pioneered by Lotus in the late 1970s, ground effects aimed at reducing the air pressure under the car. Grip was created by the low air-pressure “sucking” the car to the ground. To create ground effects, the underbody of the car was shaped like the top half of an airplane wing. The XJR-5's slim monocoque chassis allowed for large, clean wing surfaces on each side of the engine.

After many wind-tunnel tests of quarter-scale models in the Williams rolling-road wind tunnel, two underbodies were constructed. A low-drag, low-down-force version for high-speed tracks such as Le Mans and Daytona, and a high-down-force version for slower tracks.

In Trans Am spec, the V-12 engine was fed by six Weber carburetors; this setup was carried through on the GTP car. In the first full season of racing, the Webers were still used, but as a Le Mans entry came closer, work was started on a computer-controlled fuel-injection system.


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