Jaguar Releases Porsche 911 Rival: Supercharged XKR

By Motoring Channel Staff - 5/July/2006

Gaydon, England — When Jaguar introduced the all-new XK coupe and convertible in late 2005, it set tongues wagging with its provocative styling and traditional-but-sumptuous interior. One thing was missing though... It's most powerful engine type was a naturally aspirated V8 worth 224kW - not nearly enough to satisfy those drivers who want to challenge the high performance coupes from other European marques such as BMW, Mercedes-Benz and even Porsche.

But all that has changed with the advent of the XKR, which brings numerous changes to the XK range, least of which is an Eaton supercharger. The standard XK Coupe, powered by a 4.2-litre V8, takes 6.2 seconds to reach 100km/h from rest, while the new XKR with its blown V8 takes 5.0 seconds, on par with Porsche's 997-type 911 Carrera.

"Our aim when engineering the new XKR was to ensure that the car’s character remained balanced despite the significant increase in power over the normally aspirated XK," explained Jaguar’s chief engineer, Mike Cross.

"Our engineering team worked to the brief of creating a car that is 120 percent and more of an XK — the ultimate sports GT for the real world."

Like the XK model, the new XKR is built around an advanced aluminium monocoque body structure, giving the car exceptional rigidity, perfect for high speed, at-the-limit-cornering. Jaguar reckons its aluminium frame is as significant to the XKR's performance parameters as the increases in power and torque from the supercharged engine. It says the frame is unique in the industry, as it integrates the entire body structure to create a super-rigid vehicle (as distinct from an aluminium spaceframe with separate aluminum exterior panels).

To put things in perspective, the new chassis is over 30 percent stiffer than the previous XK, while the Convertible is over 40 percent stiffer. As a consequence, the XKR accelerates faster than the previous model, able to get its power to the ground more efficiently, while offering improved comfort and safety levels, such as reduced noise and vibration intrusion, and improved crashworthiness.

Jaguar also wanted customers to be able to pick an XKR from a standard XK, and the major changes include 19- and 20-inch chrome alloy wheel rims (with suitably fat tyres), a unique front apron with a bigger air dam, plus aluminium finished grille and hood vents. There's also four imposing exhaust pipes at the rear of the car and shy bootlid spoiler.

"We talk at Jaguar of how our new generation of models are ‘beautiful, fast cars’," said the director of design at Jaguar, Ian Callum. "It’s a phrase that ideally sums up our brand and can be applied to every car we design. We were extremely proud of the reaction to the new XK when it was unveiled last year – it is as beautiful as you would expect a Jaguar sports car to be. Now, the new XKR has a look that emphasises the ‘fast’ aspect of our design statement.

"The ‘powerline’ that runs from the front wheel through the cabin area and into the car’s rear haunches remains, and we have added to that latent feeling of power by adding some strong performance features such as the vents that signify the potent supercharger and the stunning new alloys that fill the wheel arches and give the car real purpose," added Callum.

As Jaguar explains, to ensure the new range-topping XK model has optimum ride and handling for the enthusiastic driver, the XKR's springs and dampers are uprated compared to the normally aspirated XK: front spring rate is increased by a significant 38% and the rear spring rate by 24%. The stiffer suspension system results in reduced body roll through corners and when allied to the Servotronic steering system, which has also been tuned both mechanically and electronically to give the steering more weight and even greater response, Jaguar assures us that the suspension translates into confidence-inspiring handling without any loss in refinement and comfort levels.

While stiffer springs and dampers are a good place to start in creating a sports car, there are many computerised systems that can make a huge difference, and company's like Mercedes-Benz have shown it is the master of electronically controlled suspension and damping systems. Not to be outdone, Jaguar has the Computer Active Technology Suspension, essentially a 2-stage adaptive damping system that ensures the optimum balance between ride and handling. The new XKR also gets switchable Dynamic Stability Control (DSC) with Traction Control System (Trac DSC), both of which have been recalibrated to cope with the additional power of the supercharged engine.

As well as the tweaked DSC systems and stiffer suspension, the XKR gets new, larger ventilated brake discs up front, while the rear discs remain the same size as the XK model - but this isn't terrible news, as the front brakes generally account for more than 65% of a cars initial deceleration. Therefore, the new front brake discs (increased from 326mm to 355mm, with 2mm more thickness) improve the braking performance of the sporty Jag, and also increase the front brake's resistance to fade. Of course, no luxury performance coupe would complete without the ABS, Electronic Brake Force Distribution, Hydraulic Brake Assist and an electronic park brake function, all of which are standard on the supercharged XKR.

And now to the section that most people are here for: the blown V8. While Jaguar's standard AJ-V8 engine that powers the entry-level XK models is getting long in the tooth, it's still a decent performer, producing 224kW or 300hp @ 6000rpm and 411Nm of torque @ 4100rpm. But with a number of tweaks that help inject new life into the aging engine, the XKR is a significantly more aggressive vehicle than it's siblings.

The addition of an Eaton supercharger and twin air intakes means the new XKR benefits from an extra 89kW (120hp) power increase over the normally aspirated 4.2-litre XK, with which it shares its basic engine configuration. Torque has also been boosted, by a serious 36% over the XK, although the overall weight of the XKR is raised by just 70kg (154lb). Consequently the power-to-weight ratio compared to the normally aspirated 4.2-liter XK is 34% higher.

Compared to the previous generation XKR model, which featured a similar engine but with less advanced systems such as variable camshaft timing, the new engine produces more power and more torque. The ultimate figures for the 4.2-litre supercharged AJ-V8 engine are 313kW (420hp) @ 6250rpm and 560Nm of torque @ 4000rpm. Jaguar claims the new 2007 XKR Coupe can sprint from zero to 100km/h in 5.0 seconds, while top speed is electronically governed to stop at 250kph (155mph). The convertible version of the XKR is about a tenth of a second slower in the 0-100km/h sprint, due to the increased weight needed to reinforce the sub structure to avoid flex.

The XKR's lightweight 8-cylinder engine has a number of features that help it generate more torque, including the most obvious, an Eaton supercharger. The water-cooled engine's cylinder banks are arranged in a 90º vee configuration and the crankshaft is supported by five main bearings and the two cylinder heads have twin camshafts apiece, creating a quad-cam engine that has 4-valves per cylinder. Jaguar says that another one of the reasons for the engine's impressive output is the continuously variable valve timing, which helps to deliver a wider spread of torque.

The air intake supply to the engine has been significantly enhanced thanks to the use of twin air inlets, and a variable inlet camshaft timing system is used for the first time on the XKR. While this feature may be newsworthy, it shows how far behind the competition Jaguar was lagging before this, which is connected with its parent company's (Ford) tightening of the purse strings. Jaguar says that in the past, the normally aspirated 4.2-litre XK has been praised for its acoustic qualities, remaining unobtrusive and relaxed at modest speeds but producing an unmistakable V8 warble when working hard. On the XKR, the noise from the supercharger threatened to dominate the acoustic character and mask the underlying sound quality, something the Jag engineers didn't want, so enhancements to the vehicles acoustic packaging were made and the supercharger noise has been reduced by 5dB compared to the previous XKR. The result is a throaty, deep V8 rumble with just a hint of supercharger whine as the revs build.

Getting the sports car's wheel-spinning 560Nm of twist to the rear wheels is taken care of by a 6-speed sequential manual gearbox, which is claimed to complete gear changes in less than 600 milliseconds - about the blink of an eye. The advanced gearbox can be driven in automatic mode, where the car shifts for you depending on road speed and throttle input, or steering wheel paddles can be used to provide a manual override for gear changes. The new gearbox has three modes to give drivers total flexibility: the Drive mode we've already covered, while the sport mode initiates adaptive software that is more determined to hold onto gears and respond to throttle inputs with more haste, while the manual mode we've also covered.

The 0-100km/h sprint time of 5.0 seconds puts the new XKR firmly in Porsche 911 territory, and though not quite as quick as the Ferrari and Lamborghini entry-level models, it provides positives in other areas, such as it's everyday usability due to the larger interior and thoughtful ergonomics. XKR drivers will benefit from acres of premium leather plus 16-way adjustable seats, and because the XKR is a car made for the enthusiast who is assumed to drive at breakneck speeds, the cabin represents what Jaguar claims is "arguably the most sophisticated driver-focussed environment of any car in its class". As well as the focus on the driver, via the ergonomics, information displays and the critical instrument displays, like any Jaguar the car gets dozens of intuitive in-car technologies, such as satellite navigation, Bluetooth functionality, a touchscreen display and keyless start, while both occupants are cosseted by a sport seat design that places much emphasis on lateral support (side bolsters) to keep the driver and passenger firmly in place during fast driving.