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Driving Dynamics - (Global)

February 16th, 2007





Driving the new XKR - exhilaration redefined

The new 420bhp (SAE) Jaguar XKR is a truly rewarding car to drive. With 120bhp (SAE) more power than the normally aspirated 4.2-litre XK and the same strong and stiff aluminium body structure, superb ride and handling is assured. Furthermore, a six-speed automatic transmission with Jaguar Sequential Shift that is regarded as class-leading in terms of speed and refinement ensures Jaguar's blend of performance and dynamics reaches new heights with the XKR.

"Our aim when engineering the new XKR was to ensure that the car's characteristics remained in balance despite the significant increase in power over the XK," explains Jaguar's chief engineer, Mike Cross. "Working with that as our base, our brief was to create 'XK plus 30%' - the ultimate sports GT for the real world.

"We wanted the performance and dynamism you would expect of an XKR but were careful to retain that exceptional blend of sporting luxury that every Jaguar must have and which is so convincingly demonstrated with the XK. The bottom line is that if you like the XK, you'll absolutely love the new XKR."

The result of that engineering brief is a car that performs vigorously in any conditions, at any speed. With superb torque at low engine speeds, instant acceleration is always available should you demand it. Similarly, the advanced steering and suspension set-up means the new XKR switches effortlessly from relaxed GT to honed sports car with ease. It is everything the XK is and much more besides.

Supercharged 4.2-litre engine

Impressive reserves of power and acceleration available in an instant are the hallmark of every great Jaguar. The new XKR ensures this by using a supercharged version of Jaguar's renowned 4.2-litre AJ-V8 engine. Producing 420bhp (SAE) at 6250rpm and 560Nm (EEC) of torque at 4000rpm, it is capable of propelling the XKR Coupe to 60mph in 4.9 seconds (5.0 seconds for the Convertible) and on to an electronically limited top speed of 155mph (250kph).

The addition of a supercharger and twin air intakes means the new XKR benefits from a 120bhp (SAE) power increase over the normally aspirated 4.2-litre XK with which it shares its base engine. Torque, so essential for instant acceleration at any engine speed, also increases significantly - by 36% over the XK. The overall weight of the XKR is raised by just 70kg, consequently the power-to-weight ratio compared to the normally aspirated 4.2-litre XK is an impressive 34% higher.

And in comparison to the previous generation XKR, the new engine produces more power and more torque. Combined with a significantly stiffer and lighter aluminium monocoque body structure, these performance improvements lead to a significant leap in the power-to-weight ratio of 12% and an equally useful jump of 7.7% in the torque-to-weight ratio. To achieve the equivalent improvements in power- and torque-to-weight in the outgoing XKR would have required nearly 50 more horsepower.

Among the benefits of the increases in power and torque are a Coupe 0-60mph sprint time reduced by 0.3 seconds compared to the previous XKR and acceleration from 50mph to 70mph in just 2.5 seconds.

At the heart of these significant performance improvements is the XKR's lightweight eight-cylinder engine with an Eaton supercharger. The water-cooled cylinders are arranged in a 90-degree V configuration and the crankshaft is supported by five main bearings. Each of the two cylinder head assemblies incorporates twin camshafts operating four valves per cylinder. One of the reasons for the engine's impressive output is continuously variable valve timing which helps to deliver a wide spread of torque. The engine uses an Electronic Return-less Fuel System (ERFS) and a three-way catalyst exhaust system for lower emissions.

The increase in power and torque over the outgoing XKR is down to two significant additions to the engine. The air intake has been significantly enhanced thanks to the use of twin air inlets, and a Variable Inlet Camshaft Timing (VICT) system is used for the first time on the XKR. By continuously adjusting the timing of the inlet camshaft on both banks of the V8 depending on the engine speed and load, Jaguar's engineers have ensured significant improvements in torque, particularly at lower revs.

The VICT system is controlled by Engine Management System (EMS) which receives engine speed, throttle position and oil temperature data from its sensors. The EMS determines the correct inlet camshaft timing by continuously referring to a digital three-dimensional map developed to provide optimum performance. The EMS then transmits the appropriate signals to two solenoids that control the degree of hydraulic force provided to the valve actuators.

Another separate characteristic that the XK has been praised for is its acoustic quality, remaining unobtrusive and relaxed at modest speeds but producing an unmistakeable V8 'soundtrack' when worked hard. On the XKR, the presence of supercharger whine threatened to dominate the acoustic character and mask the underlying sound quality. However, through enhancements to the vehicle acoustic pack, the supercharger noise has been reduced by 5dB compared to the previous XKR eliminating any potential issue.

This approach to acoustics allowed engineers to concentrate on using the exhaust system to deliver the best possible sound quality character. This was accomplished through the use of the XKR's Active Exhaust which varies the flow of exhaust gases through the main silencer box to ensure that the XKR remains quiet at cruising speeds but delivers a substantially more purposeful V8 roar under hard acceleration.

Transmission

Jaguar Sequential Shift combines all the speed and involvement of a sequential manual gearbox with the comfort and convenience of a full automatic. The system consists of steering wheel-mounted paddles and a conventional automatic gearlever, allowing the driver to switch between three automatic or paddle-operated transmission modes.

Whereas an automated manual gearbox interrupts the flow of torque during the gearchange - while the clutch is disengaged - Jaguar's transmission maintains the flow of torque throughout the shifting process. This results in gearchanges that are not only very quick, but also remarkably smooth. Gearshifts are achieved in less than 600 milliseconds, from the point at which the driver operates the shift paddle to the point at which the shift is completed.

In fact, during development, comparison tests between Jaguar Sequential Shift and rival automatic transmissions in the class showed the transmission to be the fastest system of all, changing gear at least 400 milliseconds faster than a standard automatic and 100 milliseconds faster than the best automated manual system.

The three gearbox modes give the driver total flexibility to use the transmission to match whatever driving style he or she chooses. In Drive mode, the gearbox behaves as a conventional automatic, with the software optimised for everyday driving conditions and providing all the benefits of a best-in-class automatic transmission.

In Sport mode, the gearbox's adaptive software becomes more prevalent, adapting and reacting more dynamically to demanding conditions. This software takes account of the prevailing road conditions and driver's inputs and adapts accordingly. For example, it recognises when the car is negotiating a curve, and holds the gear accordingly; Hill Recognition enables the XKR to choose the ratios to optimise the ascent or descent of a hill; the gearbox's software will also match the engine speed precisely to the engine and road speeds, 'blipping' the throttle during rapid downshifts.

Manual mode is activated by simply operating one of the steering wheel-mounted paddles, and delivers a state-of-the-art manual gear shift feel from the automatic transmission.


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