New V8 gives Jaguar XK

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500 hp Jaguar XFR debuts at the Detroit auto showBig cats have to purr, so here’s Jaguar making sure its 2010 XK and XF do exactly that.

Under the hood is a new, direct-injection 5.0-liter V8 pumping 385 hp and 380 lb-ft of torque--both numbers up substantially from the outgoing 4.2-liter V8.

Refinement is terrific and power delivery is creamy smooth--it’s easily the equal of the German competition. The exhaust even pops and crackles evocatively on the over run. Compared with the new, hard-core supercharged XKR and XFR, the naturally aspirated V8 cars ride more smoothly, despite being more focused than soft-riding Jags of old.

Sometimes 175 mph just isn't enough. That, at least, is the view of Jaguar North America, which reckons the limited-edition XKR-S sports coupe isn't quick enough for U.S. sports-car buyers.

Knowing that AMG and Porsche specials make a big impact in the United States with sledgehammer power outputs, Jaguar NA probably has its customer radar pretty well tuned. But it means U.S. Jaguar fans will miss out on the sharpest incarnation yet of the handsome XK, created to appeal to the enthusiast leanings of two engineers.

Mike Cross, Jaguar's handling guru, and Russ Varney, XK platform chief, worked out the XKR-S in spare moments as they road-tested the suspension on drives home, directing technicians to make changes during the working day.

"We developed an XK with the chassis we fancied as our everyday driver," says Cross, "a bit more focused than our typical customer would usually want but still comfortable and safe in all road conditions, including the wet."

You notice the changes as soon as the XKR-S purrs away for the first time; the steering has a meatier feel, and the ride is firmer. The headline mechanical changes are the type that might be expected on casual examination: stiffer springs and dampers front and rear, 8 percent quickened steering rack, thicker rear antiroll bar, lighter 20-inch forged alloy wheels and wider rear tires.

The forged wheels cut unsprung weight by 10 percent. The two-stage Bilstein dampers are completely revalved, the ride height dropped slightly and the variable ratio/assist ZF rack quickened by 10 percent. Jaguar also worked with Pirelli to develop bespoke tires for the XKR-S.
The effect is to stiffen the XKR-S's response and sharpen the feedback to the driver--just what enthusiasts expect.

The XKR-S doesn't have more power, but its standard 420-hp, supercharged 4.2-liter V8 is no slouch, and the new chassis makes it easier to exploit more of the performance in corners, because it gives the driver confidence, knowing that those wide rear boots and computer-controlled CATS dampers will take care of mid-corner bumps.

Even at speeds of 70 to 80 mph, Cross says the aerodynamic changes to the XKR-S bring more rear downforce and stability. Lift is reduced by 60 percent up front and 17 percent at the rear, with a 3 percent reduction in drag. The most noticeable visual change is a larger rear spoiler, still subtle, which is a big improvement at autobahn speeds (nearly 150 of the limited 200 run of XKR-Ss have gone to Germany; the other 50 are reserved for Britain).

Our main criticism is that the steering feels a little detached from what the tire contact patches are doing, in a way that a Porsche's doesn't, a comment that Cross is gracious enough not to bristle at.

"We have to work within the constraints of the basic platform, and we have an extremely driveable performance car in all conditions," is the level-headed response.

There's something else significant about the XKR-S. Jaguar is working on a facelifted XK with a new direct-injection 5.0-liter V8, to be launched mid-2009. In supercharged XKR form, this will offer close to 500 hp, and the inside line is that the stiffer XKR-S setup is a preview of this new chassis. With that in mind, customers for next year's XK are in for a special treat.