2007 Audi S6

Audi's spin doctors seem to be having trouble with this one. They tell us the S6's 5.2-liter V-10 is the "most unstressed in the class," that it has the lowest specific output among its competitors. On the other hand, Audi makes great play of this V-10's relationship with the one in the Lamborghini Gallardo. An unstressed supercar engine? Say what?

Only one way to find out: Hit the gas. There's never a moment's doubt an epic reserve of low-down torque is at play here, and the direct fuel injection wastes no time in deploying it. The six-speed auto transmission flicks the changes the instant the tach needle kisses the big seven. It ratchets speed in an effortless torrent as we careen toward the 155-mph limiter.

Effortless. And, yes, unstressed. Oh, and the noise! It has a tidal-wave quality to it, a rumbling bass drum roll of an exhaust. And though it never disappears at cruise, the depth and complete lack of harshness underway make it strangely soothing.

So although the S6's engine is roughly 15 percent less powerful than those of its key rivals, its character is someplace between the Saturn V of an AMG E55 supercharged V-8 and the frantic formula car of a BMW M5 V-10. And in a sporting sedan, that's a fine place to be indeed.

Whereas the Lambo's engine is 5.0 liters, 520 horses, and port-injected, this is bigger, torquier, direct-injected but down to 420 horsepower. The power deficit stems from the lower rev limit mandated by the torque-converter transmission. Even the bore centers of the Audi are different--wider to accommodate the bigger bore.

Although the engine is made to be ultracompact, it sits a long way forward, as the front driveshafts sprout from behind the flywheel. Then comes a longitudinal six-speed auto transmission and a center diff that directs a nominal 60 percent of the torque rearward. The aluminum-intensive suspension is by conventional coils and nonadaptive dampers. To help weight distribution, the front fenders and hood are aluminum and the battery goes to the trunk.

Given the sensational ride-handling compromise of the new RS4, there are grounds for optimism over the S6 chassis. The ride is disturbed by an unending foursquare bouncing. It's an all-speeds issue, too: Urban driving is no better. At least, unlike in past Audis, poor suspension fluidity is no bar to the handling. There's no bumpsteer or loss of grip. And the traction remains sensational. This is where the car really steps out from under the performance shadow of the M5 and E55. In the S6, every ounce of engine effort gets dispatched into propulsion.