If the latest Audi A4 feels as if it earned a masters degree in IT, then the all-new S4 double-majored in kinesiology.  Like the recently revamped Audi A4 sedan, the 2018 Audi S4 sedan packs a stupendous amount of smarts. From a lane-keeping system and adaptive cruise control that push us ever closer to autonomous cars to Audi's slick Virtual Cockpit configurable dash with Google Maps integration, Audi's compact luxury sedan is among the brainiest of its class.

The S4—and its coupe sibling, the S5—has all that, too. You may not know it from the outside, but what separates the S4/S5 from the A4/A5 is what's under the hood. Whereas the A4 uses a 2.0-liter turbocharged 4-cylinder good for up to 252 horsepower, the S4 packs an all-new 3.0-liter turbo V6 that spits out 354. That 100-plus horsepower advantage is felt in every way, and combined with other performance-oriented hardware, injects an exhilarating jolt of athleticism into what looks like an ordinary entry-level luxury sedan.

Excellent Starting Point

Make no mistake: The A4, itself all-new for 2017, is no slouch. When Audi invited us to test the 2018 S4 in Palm Springs, the company lent us an A4 to drive to the destination from Orange County, roughly 125 miles away, and an S4 for the trip back. The trip there was an excellent reminder of the standard car's abilities. The A4 more than holds its own and often even excels against rivals like the BMW 3 Series, Mercedes-Benz C-Class, Lexus IS and the new Jaguar XE. The A4 is dynamic, light on its feet, and well-balanced. Moreover, its Quattro all-wheel-drive system is legendary for its tenacious grip.

The S4 takes this platform and only makes it better. A lot better. With a 0-60 mph time of 4.4 seconds, it is well over a second faster to that benchmark than the standard A4. Standard six-piston brake calipers, meanwhile, bring this sports sedan to a stop in a hurry.

Performer in corners

But it's in between the ferocious starts and smooth stops where the S4 excels. Audis have long had a knack for corner carving, and the latest S4 only testifies to that. Driven hard on the winding Highway 243, where we ascended and descended thousands of feet in altitude into Idyllwild, the S4 danced around hairpin turns with fluidity and grace. With 369 lb-ft of torque, this engine also boasts nearly 100 more units of twist than the A4's 2.0-liter engine. This extra grunt made blasting out of corners seamless, easily getting us back up to speed. Turbo lag was all but a non-issue, only appearing rarely when nailing the throttle from a rolling start.

Rather than the 7-speed dual-clutch S tronic transmission used in the A4, Audi paired the S4's potent V6 with an 8-speed Tiptronic. This traditional automatic transmission is well-suited to the engine, and exhibited none of the low-speed hesitancy that can occasionally occur with the dual-clutch. Sorry, "save the manuals" peeps, the S4 sedan and S5 coupe are automatic only. Audi says demand just isn't there for a do-it-yourself transmission. Also, an automatic implements more readily with Audi's advanced driver-assistance features.

We spent a briefer, albeit no less thrilling, time in the S5 coupe. If not for the two fewer doors and one less seat—the S5 coupe only has room for two in its tight rear quarters—you'd be hard pressed to parse the differences between the S siblings. If mandated to judge the performance, we'd say the S4 felt just the slightest bit nimbler, which seems ironic since at 3,858 pounds the sedan is roughly 20 pounds heavier.

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Sophisticated sleeper

Back on the highway to Palm Springs and then on the return trip to Orange County and beyond, the S4 proved just as pleasing in the role of highway cruiser and urban runabout. After its initial gratifying exhaust howl getting to speed, the S4 is a quiet and comfortable compact cruise missile. If you need more proof that it can pamper, look no further than its standard front massaging seats.

Around town, the S4 is easy to maneuver, and the optional bird's-eye backup camera makes backing up or backing in to spaces far less stressful.

What you won't get from the S4 is a lot of supplemental flash when it comes to looks. Whether that's a positive or negative will depend on your tastes and, yes, even your ego. It takes a pretty trained eye to tell the difference between an A4 and an S4 (hint: look for quad tailpipes in back and a different fascia up front). For drivers seeking an understated yet handsome and sophisticated compact luxury sport sedan that packs a performance wallop, the new S4 is the pinnacle in its class.

The 2018 Audi S4 and S5 are on sale now. The S4 sedan starts at $51,875, including destination, and the S5 coupe bows at $55,575. More siblings are set to join the lineup in the form of a cabriolet and all-new 2018 Audi A5/S5 Sportback, a sleek 4-door liftback that will slot below the A7.


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