The boys from Ingolstadt have gotten serious with the 2007 Audi S6. Serious, in this case, takes the form of a 435-horsepower (DIN) V10 engine. Serious also means minimal look-at-me external clues and boy-racer add-ons. And serious means seriously fast.

When last we saw an S6 Stateside, it was a 2003 model, which only came here as an Avant (station wagon). The S6 Avant quietly disappeared from the market at the end of that year, even though that generation of A6 continued for another year until the current generation was introduced in 2005.

It's all underhood
The heart of this stealth wünderkind comes from nothing less than a supercar. Audi engineers have artfully wedged a version of the Lamborghini Gallardo's 5.2-liter V10 under the new S6's hood. It makes 435 hp (again, that's DIN — the German horsepower standard), peaking at 6,800 rpm, and belts out a similarly massive 398 pound-feet of torque, peaking from 3,000 to 4,000 rpm. Ninety percent of that broad-peak torque is available from 2,300 to 5,000 rpm.

To put that in perspective, the previous S6, with a measly 4.2-liter V8, put out merely 340 hp and 310 lb-ft of torque. These numbers are suitable for a premium sedan, but don't really distinguish an "S" model. Audi must have thought so, too, as the 2006 Audi A6 offers a 4.2-liter V8 that puts out roughly the same numbers (335 and 310, respectively).

No U.S. fuel-economy figures are available yet, but the V10's 13.4-liter/100-km fuel consumption is reportedly better than that old S6's V8 as well.

Our autobahn test-drive dreams were partially dampened (pun fully intended) by rain, sleet and snow. Still, the spray wasn't too bad, and stomping on the loud pedal produced impressive acceleration. The S6 wanted to keep running all the way up to its electronic limit of 155 mph, but we simply ran out of visibility. Unsurprisingly, blasting past unsuspecting locals on country back roads was a piece of strudel.

The really cool part was the sound of it. The folks at Audi fully exploit the wonderful and guttural growl that a perfectly balanced V10 can produce. In fact, they employ a "sound pipe" to direct carefully tuned intake noises toward the cabin. The result, when standing on it or just puttering around town, was thrilling. The noises echoing back from the many tunnels on our drive route, especially when we downshifted to bring the revs up, weren't shabby either — much more satisfying than holding our breath or honking all the way through.

Our only complaint is that the electronic throttle is a bit nonlinear and lurchy when trying to accelerate gently from a stop. We see this on a lot of cars with cableless throttles. Engineers just can't resist the temptation to use electronic trickery to make their engine feel more powerful off the line. This V10 thingy is mucho powerful, guys — you don't need to augment it. Make it intuitive.

Hooked up
Even though we had rain for much of the time, we never had any problem putting all of that power to the ground. The standard quattro all-wheel-drive system was, of course, the main help here. The conditions we encountered, combined with all of that V10 power and torque, only cemented our respect for the system.

Of course the Audi S6 was wearing pretty good shoes as well. The Continental 265/35R19 summer tires on our test car looked damn good on their split five-spoke wheels (or is it 10?). And they gripped a ton as well.

We became a bit tentative, however, when temperatures dropped and we started to see snow sticking to the roadside in the upper reaches of the course. We never had any slip or activation of the ESP system, but found it wise that Audi USA will offer the S6 with your choice of summer tires or all-season rubber at no cost differential.

Shift yeah
Some of you may complain that this new S6 will not be available with a manual transmission. But take heart, because we found the six-speed Tiptronic automatic transmission to be a good match to this V10.

You can use it three ways. Most of the time, we simply slapped it into "D" and went about our business. Sometimes, when we wanted to downshift in preparation for local-buzzing, we'd use the steering-wheel paddles. After the pass was made and we returned our brain to cruise mode, the tranny would upshift itself back to 6th. But when we wanted total command, we moved the lever to the right of "D" and used the paddles in full manual mode.

Handle it
Steering at high speeds was direct and confident. Feelwise, it was a bit less stellar in the twisties, but still precise and direct. The chassis was very well balanced, with minimal roll and excellent stability on those lumpy sorts of roads that make other cars twitchy.

But those same lumpy asphalt roads started to be a bit jarring after awhile. It feels a bit too tied down, even for a car with the "S" designation. Sure, damping is great on smoother roads with longer-wave undulations, but we wonder how the busy feel will translate to L.A. freeways and other poor-pavement areas we could name at home.

Badges?
Looking for exterior styling differences on the S6 was a bit like doing a word-search puzzle. Sure, we found the badges that say "S6" and "V10," but they didn't scream at us. It took a bit longer to find the logo-encrusted titanium trim plates on the upgraded, but not red, front brake calipers. Handsome.

There was a more aggressive front fascia, with a few more square inches of air intake under the lights, a new under-nose duct and a deeper lip. The lower edges of the doors had subtle spats, and the rear cap was tweaked to allow for four chrome exhaust tips.

Some of the more observant locals in the small German villages we drove through noticed the car, but not many. We assume the same would have been true of local law enforcement. Excellent, Smithers.

Inner beauty
Inside, Audi's S6 was a decidedly nice place to be. Sure, it had many of the same shapes as the A6, but the materials used looked purposeful and inviting at the same time.

The seats were wonderfully contoured and had a slight, but not overpowering, racing-seat look. They grabbed onto us well, too, thanks in part due to the covering, which was a combination of leather and Alcantara pseudo-suede. It looks striking, and it works. But according to Wolfgang Hoffmann, Audi USA product planning director, American cars will get 100-percent leather seats, due to local market research.

We also liked the tasteful carbon-fiber inserts on the center console and door accents. Just enough, and if it's fake, don't let Audi start printing 20s. Silver accents and speaker grilles contrast nicely with the carbon and titanium color of the instrument panel. Wolfgang explained that carbon will be an option, with Birchwood standard.

When can I get mine?
As one might expect with a European first drive, U.S. sales are still a ways off. Audi S6 sales will kick off Stateside in November. Since there are a few months to go, pricing has not been announced, but Wolfgang told us that a typically equipped S6 will probably go slight upward of $75,000. Oh.

Bottom line: The 2007 Audi S6 is a serious sport sedan, with a serious V10 engine in it. It is a well-engineered piece of work — seriously.