Full-size luxury doesn't come without a cost--in price, or in weight. So while the Audi A8 weighs between 4,400 and 4,800 pounds, it's one of the lighter vehicles in the super segment it calls home. As with the Jaguar XJ, the A8's heavy use of aluminum lightens and brightens its entire performance, endowing it with assertive handling and relatively great gas mileage, and absolutely great fuel economy with its new turbodiesel engine.
This year the A8 offers up a handful of powertrain choices. Four different engines come in five different outputs.
With either long- or short-wheelbase cars, Audi offers a basic supercharged 3.0-liter V-6. It's scored at 333 hp and teams-as all A8s do-with all-wheel drive and an 8-speed, paddle-shifted automatic. With a little more vibration and noise than necessary, the V-6 pumps out prodigious low-end torque on its way to a 5.5-second 0-60 mph run and a top speed of 130 mph.
A new turbodiesel offers up 240 hp and 406 lb-ft of torque for 0-60 mph times of 6.4 seconds and initial EPA ratings of 36 mpg highway. This engine has been implicated in VW's emissions-cheating scandal, and Audi has set up a web site for owners who need more information about repairs and buybacks.
Back in the gas-powered spectrum, the A8 stuffs in a twin-turbo 4.0-liter V-8 with 420 hp and 444 lb-ft of torque, adopting a more visceral feel and dropping 0-60 mph times to 4.7 seconds. The same basic engine twists out more turbo boost in the S8 for a total of 520 hp and a 0-60 mph time of 3.9 seconds, as well as a 155-mph top speed.
Atop the A8 range is the luxuriant torque and odd cylinder arrangement of the W-12 flagship engine. The 6.3-liter 12-cylinder pumps out 500 hp and 488 lb-ft of torque, pushing the sedan to 60 mph in 4.4 seconds.
The A8's automatic is a joy. Audi's calibration ensures almost perfect shifts with smooth engagement, and fuel economy of up to 29 mpg highway in gas-powered cars. Multi-gear downshifts are a snap with either a heavy foot or a quick finger on its paddle shift controls.
The all-weather traction of its all-wheel-drive system is a big part of the A8's composed handling. Audi splits torque 40:60 front to rear, and the system can shift more power to the front (up to 60 percent) when traction slips at the rear. On the S8, a separate rear differential can move power side to side to help cornering and traction. The same diff can be had on other models in a Sport Plus bundle, packaged with adaptive dampers, summer tires, and variable-ratio steering.
Drive Select is Audi's way of saying "tune it yourself." The system toggles through various comfort, sport, and automatic modes to change the behavior of the car's steering, suspension, throttle, and transmission. It can't help, say, to introduce more feedback in the A8's steering, but it does help coordinate and tailor these systems so, for example, soft damping doesn't have to mean slow steering.
The S8 is our pick here. It's not truly a sport sedan, not at this size and not at 4,500 pounds on the curb. In its class it feels like a sprinter, one with a compliant ride and just enough body lean to blend its flagship mission with the ability to exit highway off-ramps at triple-digit speeds.