The new 5.0-liter V8, designed in-house unlike the previous 4.2-liter, is the 2010 XK big improvement, by cat-like leaps and bounds.   The previous 4.2 has been left in the dust by the new 5.0-liter V8 that's more compact, more efficient and much more powerful, using recent advancements in engine design.   The new engine is the third generation of Jaguar's AJ-V8.   Jaguar, being freshly sold by Ford to India's Tata Motors in the spring of 2008, produced this engine in-house at Jaguar facilities in Coventry, England.  

It's an all-aluminum 32-valve V8 featuring direct injection, independent variable cam timing, cam profile switching, and a variable geometry inlet manifold.   Jaguar raises the bar, literally, with this multi-hole direct injection system that sprays pressurized fuel (up to 150 bar) dead center into the combustion chambers.   The variable camshaft timing system has its own Jaguar spin, as well.   And the naturally aspirated engine has inlet camshaft profile switching, changing the characteristics of the engine for the torque, power or economy that may be needed at any moment.   The air intake has been totally redesigned, eliminating the supercharger whine, and also the view of the engine.   All you'll find under the hood is a blank sea of black plastic.   Call it progress.   It works by selecting air tunnels among 14 of them, varying from 27 inches (low speeds) to 14 inches (high speeds).   Progress indeed.  

The engine's bottom line is an increase in horsepower of 29 percent for normally aspirated and 23 percent for supercharged; also a big increase in torque, same fuel economy, and slight reduction in CO2 emissions.   In a nutshell, all of these technological advances improve throttle and/or engine response, torque, fuel economy and emissions.   Not to mention horsepower, i.e.   speed.  

On that subject, the XKR has a new sixth-generation twin vortex supercharger, leaping with the engine, technologically speaking.   Remember the buzzwords: twin vortex.   The Roots-type unit uses two water-cooled intercoolers, and raises thermodynamic efficiency by 16 percent.  

The specs are: 385 horsepower and 380 pound-feet of torque at 16/22 miles per gallon in the normally aspirated XK, and 510 horsepower with 461 pound-feet with 15/22 mpg.  

The XKR can accelerate from 0 to 60 in 4.6 seconds, boosted by that humongous 461 pound-feet of torque coming on strong at 2500 rpm; it will effortlessly reach 155 mph where it wants to keep on running but is electronically limited.  

With your foot on the pedal, you will have no complaints with the normally aspirated engine making a mere 385 horsepower.   Nor will you have any complaints when your foot is off the pedal, after you climb out smiling.   Even the exhaust note, which Jaguar calls the sound track, has been addressed in great detail.   We can't say it exactly rumbles, but Jaguar says its engineers have accentuated the acoustic feedback into the cabin in order to further enhance the driving pleasure.   Intake manifold pressure pulsations are fed into an acoustic filter at the rear of the engine that's tuned to provide a crescendo at high revs.   The 6800 rpm redline is some rush.  

The XKR will get you past a semi-truck on a two-lane highway as quickly as almost anything on wheels that's longer than a superbike.   Give or take a tenth.   Since the supercharger has stopped whining, some of the thrill is gone; now it's sheer semi-silent speed.   Since now you're not whooping at the whine, you can feel your jaws stretch back from the G-force of the acceleration.  

The regular XK uses the same engine without the blower, and makes 385 horsepower with 380 pound-feet of torque.   In addition to the miles in our test model XKR, we got good seat time in an XK, including one hot summer night run in a top-down XK over 120 miles of scarcely traveled two-lane along the Columbia River: a memorable drive.   It's what you own a Jaguar for.   Not once did we find 385 horsepower lacking.  

If you're looking for mention of shortcomings in the XK's engine, transmission, chassis, suspension or brakes, you won't find them here.  

The brakes, for example, are massive 15.7-inch rotors with six-piston calipers in front, and 13.8 inches with four-pots at the rear.   If those don't stop you nothing will.  

The six-speed automatic in Sport mode with paddle shifters is all you'll ever need.   Shifts are sharp, quick, and on time; and there's downshift rev-matching, meaning the engine will blip for you, quite nicely.   There is no manual transmission; Jaguar fans of tradition will just have to get used to today's Jaguar.  

Underway, the XK feels solid, stable and planted.   The XK chassis is quite stiff, a benefit of its riveted and bonded aluminum construction.   This stiffness is the key to the XK's silky smooth ride and demonic cornering.   Another byproduct of the stiff chassis is the steering accuracy, tight and quick but not skittish.   Working with that superb chassis is double wishbone suspension front and rear.   The XK has never handled better.  

The latest generation of Adaptive Dynamics replaces the Computer Active Technology Suspension (CATS) that offered two modes, soft and firm.   The Adaptive Damping System provides continuous variable damping between those two, for ride comfort or maximum cornering on rough roads.   The definition of continuous: chassis motion, including roll rate and pitch rate, is analyzed and adjusted 100 times per second.   Meanwhile, wheel travel is analyzed and corrected 500 times per second.  

With the Dynamic Stability Control System, the driver can choose Normal, Dynamic (formerly known as Sport), or Winter mode.   Throw in Active Differential Control, the electronic version of a mechanical limited-slip differential, for more traction on snow or ice.