Jaguar XKR, More Power And Lower CO2 Emissions

There's a new heart in the Jaguar XKR supercar a roaring 5-liter V-8 which is slightly smaller than the old 4.2 liter mill, and in supercharged form chucks out 510 bhp. Or, you can opt for the XK, which gets 385 bhp without the supercharger.

Thanks to the new engine, coupled to a modified version of the ZF six-speed auto, the 0-60 mph time is down to a very quick 4.6 seconds. This supercar will leap from 50 to 70 mph in just 1.9 seconds, which gives an idea of on-the-road response.

225 mph - without speed limiter

Top speed is limited to 155 mph (250 km/h), but Jaguar says that the new XKR is good for 225 mph without the speed limiter. That top speed, matched by the XF sedan, will raise a few eyebrows because many very expensive supercars and exotic cars, including the Porsche Carrera GT and Pagani Zonda only claim top speeds of 205-215 mph. This shows that the aerodynamics of the Jaguar XKR are pretty good.

Of course for almost all buyers this is academic, because unless you go on a race track it is very difficult to find anywhere you can drive a 150 mph, let alone 200 mph, apart from some German autobahn which are hardly up to it and a few other places.

Minor changes to body

The new Jaguar XKR supercar looks a little different, too. The side air intakes for the brakes are reshaped, and the lamps have been removed from them. They are now deep, narrow intakes, which improve appearance. The pair of

louvres in the hood are reshaped slightly. At the rear, there is still just a small spoiler, and four exhaust pipes, so the the car is hardly changed. However, there are LED rear lamps which are more distinctive.

Inside, the car is not much changed, except for the addition of the Jaguar Drive Selector, a rotary knob on the console, first introduced on the XF. Also, you can have heated and cooled seats if you want.

Stunning engine acceleration

The big news is that the AJ-V8 Gen III 5.0 liter V-8 is a real powerhouse, churning out 510 bhp at 6,000-6,500 rpm, with maximum torque of 461 lb ft (625Nm) all the way from 2,500 to 5,500 rpm. This is interesting because the proponents of modern turbos say that a wide spread of maximum torque is one their advantages. Not so, it seems.

In fact, this is a sixth-generation Roots-type twin vortex blower, which works through a pair of warter cooled intercoolers. Jaguar says that the new blower is 16% more efficient than the old one and is virtually silent – you might actually miss that distinctive supercharger whine.

This new engine, which has been a few years in development, is based on a high-pressure aluminum diecast cylinder block, and cylinder heads cast from recycled aluminum. The crankshaft is a spheroidal graphite casting, while the connecting rods are steel forgings.

The new engine is about one inch shorter to the old one, and a little lower, owing to changes in the intake system.

New direct injection system for high efficiency

The main feature, though, is the direct injection system. Jaguar has opted for multi-hole injectors mounted in the middle of the cylinder heads. Fuel is injected at 150 bar – about 2,200 lbs per square inch – which ensures good distribution and rapid combustion at low speeds. This high-pressure injection results in a cooler chamber which allows the use of higher compression ratios – 9.5:1 for the supercharged engine – and more power.

Variable valve timing

Variable valve timing in which the opening point is advanced or retarded according to conditions is used on all four camshafts. In addition, the naturally aspirated V-8s get two-stage valve lift. Each camshaft has three cams per valve, and a two-piece tappet – similar to the Porsche system.

At low lift – 0.22 in (5.5 mm) and 214 degrees opening period – the low-lift cam is actuated by the central part of the tappet, and at higher speeds, the system switches to the outer part of the tappet and the high lift cams, which give 0.41 in (10.5 mm) lift and 250 degrees of opening. The engine speed when the switching takes place depends on the load.

Coupled with Jaguar’s improved six-speed automatic gearbox, and the lightweight of the new aluminum body, this engine will give you terrific performance. The auto has been improved to handle the extra power, and there is a new electronically controlled limited-slip differential, which ensures that the torque always goes to the wheel with the most grip.

Stiffer suspension

The distinctive feature of the XK suspension is its combination of suppleness and comfort with good handling. The active damping system has been upgraded again, and now probably limits that crash-through that could occur at speed on some very demanding switchback roads

The supple suspension works in conjunction with a modified version of the stability control to give enjoyable, responsive handling.

Overall, the new Jaguar XKR is now an even faster supercar, yet giving pretty good fuel economy of 15/22 mpg for the EPA city and highway ratings against 15/23 mpg for the 4.2 liter model. Performance is pretty stunning, too.

It is a pity that the larger engine and beefier transmission and extra odds and end have pushed the weight up by 194 lb (88 kg). In fact, the more sporty customers would now like a short-wheelbase two-seater, as well as the 2+2, with a little less luxury equipment, to get the weight down to 3,500 lb (1,590 kg) for sportier handling and even better acceleration.

Even so, the new Jaguar XKR looks as brilliant as ever, has better performance, and will still set the standards for ride and handling in supercars.