Originally Posted by whiteSTR

Thats Trans Am, but there is also the GT3 SERIES.. THIS IS THE CAR THAT WE NEED TO LOOK AT...



In the GT3 series it's Apex Motorsport with the new XKR GT3. In September 2006 Richard Lloyd’s Apex team signed the contract with Jaguar to build and run XKRs in the new FIA GT3 championship. This is not, however, a factory motorsport program and the Apex race activities are independent of Jaguar.

The XKR GT3 retains the same supercharged, 4.2 ltr quad-cam V8 engine as the road going car. The rules allow for alterations to some key components on the basis of durability, and Apex has made some modifications to increase power, now reckoned to be generating around 500bhp.

Cooling is achieved through the use of an air-to-water cooler mounted low down in the nose of the car to cool the water from the standard supercharger charge coolers, with an oil-to-air cooler mounted behind that for the dry-sump oil system. The main engine cooling duties are handled by an NRP aluminium radiator mounted in the standard factory position.



Engine intake air is drawn from vents mounted on the front corners of the car’s nose through a custom carbon fibre box holding the air filter before being fed through to the supercharger.



Power is transmitted to the rear wheels via a carbon propshaft to a 6-speed Hewland sequential transaxle in the rear. Since none of the road going XKRs come with a manual gearbox, this was something that needed to be changed anyway. This change also resulted in an enhancement to the car’s balance by altering the weight distribution slightly to the rear.

The suspension has also been altered by Apex. Using unequal-length double wishbones on all four corners and specially fabricated anti-roll bars, controlled by Koni two-way adjustable coil-over shock absorbers, the car is given a well balanced and reasonably easy handling style. Since professional drivers are disallowed by the GT3 rules this suits the majority of drivers likely to race the car.



Braking at the front is controlled by Alcon six-pot calipers wrapped around 375mm discs, and at the rear Alcon four-pot calipers with 330mm discs. Apex use an AP Racing floor-mounted, adjustable brake bias pedal assembly, with the bias control mounted on the central column below the electrical switches.



GT3 specifies the use of a control Michelin tire in the championship, though some leeway is given on width. Maximum diameter is fixed at 18 inches, since Michelin don’t manufacture 19 or 20 inch tire. 11 inch wide OZ cast magnesium rims are used front and rear. Since the races are all one hour in length, and the drivers are non-professionals, putting wider rims on the rear could be counter-productive. The narrower rims allow the tire to heat up faster at the start of the race.



The car uses the same lightweight aluminum chassis as the road car. All the interior is stripped from the car and a steel roll-cage is fitted to protect the driver. The wiring loom and all computers are removed and replaced with a custom loom (the wiring alone saves 25kilos of weight).



Although the reduced weight of the all aluminum chassis is not such an immediate advantage, given the additional weight penalties imposable by the FIA, its sophisticated bonded and riveted structure makes the car very responsive to suspension and set-up changes.



The main Achilles heel for the XKR GT3 could prove to be the use of the standard Jaguar supercharger: a Roots type blower, where air is forced into the engine using two helically formed counter-rotating rotors. Roots blowers are relatively inefficient, producing the most charge air heat for a given amount of boost pressure compared with a Lysholm twin-screw supercharger. Keeping the charge air cool at high revs, over a one hour race in hot weather, could prove to be problematic. During a warm testing day at Donnington Park, modifications were being made to the air ducting over the coolers and heat reflection away from the intake box for just this reason.