Since there's been some confusion in the past, let's set off by getting our branding barometer calibrated. Audi A4: Entry-level sports sedan. Audi RS4 (due out late next year): High-po competitor to the M3, Mercedes-Benz C63 AMG and Lexus IS-F. Audi S4: Well, that gets a bit sticky...

Audi cites the S4's main competitors as the BMW 335i and 335xi, the Mercedes-Benz C350 and the Lexus IS350. You'll notice one of these things is not like the other.



With the exception of the 335xi, none are equipped with Audi's party piece: all-wheel drive. Naturally, that feature comes at a cost. Starting price of the 335xi: $42,300 with a manual and $43,625 with BMW's Steptronic auto 'box. Starting price of the 2010 S4: $45,900 with a six-speed manual or $47,300 with Audi's new seven-speed S tronic dual-clutch transmission. That's a minor price discrepancy, but a discrepancy nonetheless. So what's the extra coin get you?

If you want to debate whose all-wheel drive system is better, feel free, but we'll save you the trouble: Audi, by a landslide. BMW's AWD option is aimed at snow-bound Northerners; Audi's is a performance upgrade and a brand differentiator. Quattro's been honed to perfection over the last 30 years and, at the end of the day, it's just what Audi does – and they do it properly.

Those interminable days of relentless understeer are nearly a thing of the past, replaced with smooth tracking and seemingly limitless grip. But as we found in review of the 2009 Audi A4 3.2 Quattro, it comes at the expense of engagement. With the S4, Audi sought to rectify the situation by focusing on two things and two things alone: tractable power and enhanced agility.



The first part of the formula comes from the all-new supercharged 3.0-liter TFSI V6, initially offered Stateside in the 2009 Audi A6. Retuned from its upper-midsize sedan sibling, the four-rotor equipped supercharger huffs and puffs 11.6 PSI into the bent six's cylinders, resulting in 333 horsepower at 5,500 RPM and 325 pound-feet of torque from 2,900 to 5,300 RPM. For those keeping track, that's seven horsepower less than the previous 4.2-liter V8, but 23 lb-ft more, all while returning 18 MPG in the city and 27 MPG on the highway (28 MPG with the S tronic). Its gas-guzzling predecessor only managed 13 city/19 highway.

Twist the key and Audi's (overly bitched about, albeit misleading) decision to slap a "T" onto the fenders of its supercharged sedan strikes as a tactical move more than a confusion creator. With the exception of a nearly imperceptible wine from around 2,000 to 3,000 RPM (seriously, had to stick our head out the window), Audi's boosted six does its best impression of a B-movie thriller: it's quiet, too quiet. Thankfully, aural pleasure isn't derived from the lump under the hood. The twin-tipped dual exhaust elicits the slightest burble when mating the throttle to the floor and delivers a pleasing, fuel-drunk "burp" when equipped with the S tronic tranny.



No matter the gearbox, you'll be thoroughly pleased by the shifting experience. The six-speed manual goes together with the supercharged mill like chicken and waffles, while the seven-speed S tronic – the first application on a longitudinally mounted engine from Audi – adds a healthy dose of Vermont's finest maple syrup. Clutch take-up is a bit on the high side, but full acclimation is just a few shifts away, and with the S tronic, Audi continues to prove that commuters and back-road bombers can live together in harmony with a singular gearbox. In full automatic mode, gear selection is intelligent and unobtrusive – even when it reaches for the ultra-tall, fuel-saving seventh ratio – and when twisty time comes, the steering wheel-mounted paddle shifters are more than willing to engage the proper gear based off the only computer we tend to care about: the gray stuff between our ears.

Audi cites a 0-60 MPH time of 4.9 seconds with either the manual or the S tronic, although dialing in your own revs and dropping the clutch with a wanton disregard for mechanical sympathy may deliver slightly quicker times. Regardless of the initial sprint, the new mill's mid-RPM punch picks up where the outgoing V8 left us cold, with a blissfully flat rush of acceleration from 2,000 RPM until around 6,500 RPM, just before the fuel cutoff kicks in a few ticks past the seven-grand redline. Compared to the A6, where its 300 hp seems merely adequate to lug 4,123 pounds of luxury, the 3,874-pound S4 scoots along with quickness, delivering that Germanic missile-guided bank-vault sensation.

But focusing on thrust sells the S4 short. More than any other element, the Sport differential is Audi's pièce de résistance. Coupled with the RS4-inspired rear bias all-wheel drive system (standard 40:60 front-to-rear, with a maximum of 80% sent to the rear), the trick electronic diff – similar to the unit found on BMW's new line of xDrive products – shuffles torque to the outside rear wheel, pushing the car through the bend without relying on ABS-based nannies to heat up the brakes and spoil the fun.



We had the chance to test the S4 with the Sport differential on both an autocross course and through some of the rolling hills around Sonoma's Infineon Raceway, and came away with a two realizations: 1) It's even better than the unit fitted to the positively porky but sickeningly entertaining BMW X6 M, and 2) All the reports of the new S4 "stepping its tail out" on corner exit are daft. Yes, it feels that way, but it simply isn't.

While running around the cones with the Audi Drive Select system set to Comfort, the S4 pushes similarly to the A4. In short: a predictable buzz-kill. However, switch the ADS to Dynamic, disable the stability control and the S4's entire attitude changes. Although we heard some journos still complaining about understeer, we found the proverbial "slow in, fast out" to be the perfect way to attack the bends. Tip into the brakes early, turn in and then start slowly feeding in the throttle. Give it the boot just past the apex and you can feel a measured dose of twist being delivered to the proper wheels. The back end slips slightly and by the time you've straightening the steering, you're riding the red mist towards the next corner. It's thoroughly engaging and completely annihilates one of our primary criticisms of the standard A4.



Out on the track, this time in a Sport diff-less manual model, the core components of the S4 show through. The stiffer springs drop the S4 nearly an inch over optional 19-inch wheels (we've got 18-inchers on our tester with 245/40 rubber), and the additional tire camber and speed-sensitive steering tweaks make the S4 supremely confident around the circuit. Bombing bend after bend, low-speed left-handers and high-speed sweepers are dispatched with a minimum of drama, and although the steering is noticeably more precise than the A4, it still lacks some of the feedback we crave.

Our only real issue stems from the brakes, which have been upgraded from 12.6 to 13.6 inches in front and from 11.3 to 13.0 inches in the rear. After three laps of flogging, pedal feel got progressively mushier and stopping distances increased to sphincter-sucking-seat status. We wouldn't call the S4 a tried-and-true track tool, but with some upgraded pads and stickier rubber, it could easily handle the task.

Back on public roads, the S4 delivers on its mission of being a sports car in a staid sedan's clothing. Few exterior elements distinguish the S from the A, so aside from the tweaked front and rear bumpers, grille, trunk spoiler, aluminum mirrors and standard LED taillights, you're free to fly under the radar of the local constabulary. Even the lowered suspension does little to affect ride quality and interior noise, and on the inside, the gray gauges, black headliner and bolstered seats are a welcome addition to a cabin we've previously praised. The one demerit we would issue is for the window switches, which appear to have been swapped out with lower cost units that feel slightly cheaper than what we've grown accustomed to with Audi. Yeah, we know it's a minor gripe, but we just want ensure it's not a sign of things to come with an otherwise faultless interior (previously voiced MMI issues aside).



Surprisingly, that last point is telling about the overall S4 experience. In the past, if you wanted a forced induction, all-wheel drive monster with telepathic abilities that can make even the most hamfisted feel like driving deities, you were left with a singular option: the Mitsubishi Evolution. However, some of us actually want to enjoy our time inside and stay on the DL while doing it. Cheap plastics, wonky switchgear and a comically oversized (if functional) rear wing are fine when you're 25, but not when you're looking for an entertaining way to end your day while toiling away in Middleagedom. So what Audi's created is an Evo for the discerning, low-key enthusiast. A sports sedan you actually want to drive, but aren't forced to. And on that measure, they've succeeded – brilliantly.



Photos copyright ©2009 Damon Lavrinc / Weblogs, Inc.