And if that isn't enough, you can raise the ante with a 6.0-liter 12-cylinder engine. New for 2005, the A8 L 6.0 gets Audi's unusual W12, which is actually two single-cylinder-head VR6 engines, splayed like two Vs and mated at the crankshaft. Each bank has its own computer controls and throttle.
Other things equal, is this W design more powerful or economical that a conventional V12? Not really. Torque and horsepower are comparable to the 6.0-liter V12 in BMW's 760Li. The 6.0-liter V12 in the Mercedes S600, with its twin turbochargers, is substantially more powerful than either the Audi or BMW engines.
The advantage of the W12 lies in the packaging. Despite its extra cylinders, it is no bigger than the typical V8 with less displacement. Indeed, Audi's W12 is actually a bit smaller by overall dimensions than the smaller-displacement V8 in the A8 4.2. The W12 therefore allows Audi to build a 12-cylinder sedan with all-wheel drive. With a conventional V12, there would simply be no space in the engine bay for a differential and other components required to power the front wheels, according to Audi.
Regardless of the packaging advantages, the A8 L 6.0 is a blast to gas. Throttle response is immediate, and it delivers acceleration-producing torque in a wide, flexible band befitting a luxury carmaker's flagship sedan. The W12 pulls hard up to its 6200-rpm redline, and it feels like there's still more power coming when it hits the rev limiter. Moreover, the revs translate to executive-class thrust. Audi reports 0-60 mph times of 5.0 seconds, with top speed governed at 155.
With either engine, the A8's six-speed automatic shifts up or down according to the driver's wishes, deftly sensing how quickly and how hard the throttle is mashed. Upshifts are silky smooth in full automatic mode; in some instances, downshifts could come quicker, but the reserve of torque in either engine more than compensates for any shift lag. This transmission is an improvement in every respect over the A8's previous five-speed automatic. It helps the A8 achieve better fuel economy with the improved acceleration, and V8-powered variants are no longer saddled with a federal Gas Guzzler Tax.
The automatic also features Porsche's Tiptronic system, allowing the driver to slide it into a manually controlled mode. Manual shifting is never necessary, because the transmission is quite responsive in the automatic mode, but it can be a whole lot of fun. Here, however, we lodge a small complaint. Even in manual mode, the transmission will shift up at high rpm, rather than holding the selected gear. That seems to defeat the purpose of giving the driver "manual" control to begin with.
The A8 features adaptive air suspension at all four corners, and it's a bit more sophisticated than the rear air shocks that could be inflated on 1970-vintage American station wagons. Four settings are available, selected electronically with the MMI. There are genuine differences in ride and handling with the basic Comfort and Dynamic settings, but neither is uncomfortably firm nor disappointingly mushy.
In the Comfort mode, the A8 rides at the normal ride height (120 millimeters or 4.7 inches). "Comfort" might suggest a cushy, mushy ride, but that's not the case. Even on a narrow, undulating Kentucky backcountry road, we found the suspension well controlled with Comfort selected, yet still smooth, compliant and comfortable. Switching to the Dynamic mode lowers the suspension by 20 mm (about three-quarters of an inch). You might think Dynamic is buckboard firm, but we found it quite comfortable and compliant, though tuned for sporty handling and more aggressive driving. Both modes operate at all speeds, or you can switch to the Automatic mode. Here the system tailors the suspension damping to conditions and the way you're driving, automatically lowering the car at 75 mph. This is usually the best setting, as the system continuously matches the ride and handling to the situation, and does a good job of it. The ride is smooth and supple, without the slightest sensation of floating or wallowing. Lastly, there is the Lift mode, which raises the suspension 25 mm (about an inch) above the normal ride height. Lift is a good setting for gravel roads, snow, nasty driveway or garage transitions and other situations that call for a raised ride height. Exceed 62 mph in Lift mode and the suspension automatically lowers to the normal ride height.
Besides offering excellent traction in slippery conditions, the A8's quattro all-wheel-drive system improves stability when cornering, whether under full-throttle acceleration or when the driver lifts off the gas suddenly in the middleof a turn. Quattro also eliminates torque steer, that pulling sensation on the steering wheel that powerful front-drive cars often exhibit under acceleration.
Despite its length and substantial weight, the A8 is impressively agile, and bears up well under truly aggressive driving. The steering is sharp and precise, providing excellent communication between the tires and the driver. One key to this big sedan's excellent handling and ride quality is its rigid aluminum space frame. The frame resists flexing and lets the suspension do all the work, which is how it's supposed to be. That's why the A8 delivers such a nice balance of fine handling and ride comfort. Driven to the limit in a corner, it understeers a bit, tending to push toward the outside edge of the pavement. To counter this, the driver simply lifts a little from the throttle, and the front tucks in and tracks through the turn. It works beautifully.
The A8's brakes are easy to modulate for smooth stops, and powerful enough for repeated hard braking from high speeds without fading. The electronic brake-force distribution (EBD) re-proportions braking force from rear to front as weight inevitably shifts forward during braking. If needed, Brake Assist will sense a panic stop and apply maximum braking even if the driver hasn't fully depressed the pedal. The A8 exhibits very little nose-dive during braking and absolutely no drama in the hardest stops. It simply stops straight and true, allowing the driver to maintain steering control in virtually all circumstances.
The A8's Differential Lock helps assures stability even while turning under hard acceleration. An electronic stability program (ESP) compares vehicle behavior against driver input, and uses the antilock brakes and traction control to correct a skid or slide. Add quattro all-wheel drive, and the A8 will do everything physically possible to keep you heading where you want to go. In an emergency situation, just remember to stand on the brakes, don't relieve pedal pressure, and look and steer where you want to go. Next Page