When we first saw Audi's sexy S5 coupe (on architecture internally known as B8 in 2007 as a 2008 model), we fell in love with the car's Coke-bottle profile, near-perfect proportions, and the company's brilliant 4.2-liter V-8 that made 353 baritoned horsepower. Later updated with a 333-hp supercharged V-6, we felt the car had lost some of its masculine mystique. However, we're already on record as fans of Audi's current A4 2.0T quattro, which recently took second place in our Big Test of compact luxury sport sedans. Despite it being the quickest of the bunch in both straight-line acceleration with its 252-hp turbo-four and around our figure-eight test with its all-wheel drive, we said the A4 lacked the personality to take the top spot. If that A4's 0-60-mph time of 5 seconds flat didn't blow your hair back, Audi has just the thing: the 2018 Audi S4 with a 354-hp 3.0-liter turbocharged V-6 shoehorned into the same competent chassis but with a retuned all-wheel-drive system, as well as the other B9-chassis stable mate, the 2018 Audi S5.

Measuring Up

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Because there are many similarities, hence the double-car First Drive, it's tempting to assume Audi's five-passenger S4 sedan and four-passenger S5 coupe are merely four- and two-door versions of the same car. Besides the door disparity, a quick glance at specs shows a 2.4-inch variance in wheelbase, 2.1 inches in length (S4 is longer), and small differences in width and height (the S5 is slightly wider and lower by about an inch). It's worth mentioning that the S5 is also offered in Convertible and four-door Sportback (hatchback) variants. As expected, the sedan has a 1.3- and 3.0-inch advantage in rear head- and legroom over the coupe. Plus, its trunk is 1.4 cubic feet larger than the coupe's.

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Unlike the A4/A5 twins, and because they are intended to be above-premium sport-oriented cars, there are no front-wheel-drive versions, and the all-wheel-drive system is biased 40/60 front to rear. For these models, Audi continues to exclude the usual Premium base trim level and only offers Premium Plus and Prestige for both the S4 and S5. As such, standard equipment levels are generous and thorough: an intelligent key (locking and ignition are keyless), a sunroof, full LED headlights/taillights/DRLs and interior lighting, auto-dimming mirrors, Audi Drive Select (Comfort, Auto, Dynamic, and Individual modes), Alcantara trim, 40/20/40 split-folding rear seats, a rearview camera, low-speed automatic braking, and heated leather front sport seats with powered eight-way adjustability, diamond stitching, power side bolsters, and massage. There's also satellite and HD radio, Bluetooth, and two USB ports that access Apple CarPlay/Android Auto as standard. The S4 gets a 19-speaker Bang & Olufsen sound system, which is optional on the S5. Both come with three-zone auto climate control and eight airbags to keep passengers comfy and safe.

The S4 and S5 test cars we drove were identically trimmed Prestige variants with the same options. They included Audi MMI Navigation Plus with touch, a color head-up display, a top-view camera system, and Audi's benchmark reconfigurable virtual cockpit instrument panel, which supports Google Earth mapping or a constellation of displays/gauges.

New Engine; new transmission

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Last year's S4 and S5 quattros were powered by a 3.0-liter supercharged V-6, and gear changes were handled by either a six-speed manual or a seven-speed twin-clutch automatic transmission. All that's changed for 2018. The new driveline consists of a re-engineered 3.0-liter V-6 (now turbocharged) and an eight-speed automatic. There weren't enough takers for a manual transmission last time, so blame your "I don't want to be bothered with a third pedal" neighbors for that. Rest assured, however, the cars' new eight-speed automatic shifts with the same quickness and seamlessness as the previous seven-speed twin-clutcher. It also performs the same throttle-blipping matched-rev downshifts with ease. Displacing the same 2,995 cubic centimeters, the new engine opts for the so-called hot-V configuration, where intake is on the outer portion of the engine and the exhaust manifolds feed the single twin-scroll turbocharger that nests inside. The net result is output that increases by 21 horsepower and a not-insignificant 44 lb-ft of torque. Audi claims a 4.4-second 0-60 time, but we already clocked a 2013 S4 with that very acceleration and beat the beloved V-8 powered 2008 S5. We're betting the 2018 S4/S5 quattros will reduce the time to 60 mph by at least 0.2 second. At the same time, fuel economy has improved, as well. The previous supercharged S4/S5 cars earned 18/28/21 mpg city/highway/combined with the seven-speed. The new turbo eight-speeds get 21/30/24 mpg ratings from the EPA.

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Both S4/S5 ride on the same multilink front/rear sport-tuned suspensions and standard 8.5-by-18-inch alloy wheels and summer tires. Our test cars instead wore optional 19-inch wheels ($800), and both featured the S Sport package ($2,500), which includes adaptive/adjustable suspension and red brake calipers clenching the standard 13.8-/13.0-inch vented discs. More important, it also includes an electronically controlled sport rear differential that actively (and noticeably) shifts torque between the rear wheels.

German Pointer

Unless variable-ratio steering is linked to the amount of dial on the steering wheel itself (more turn, quicker ratio), we're generally opposed to systems that only take their orders from vehicle speed. They tend to provide incongruous responses and behave unpredictably. Yet both of our test cars featured Audi's optional dynamic steering systems ($1,150), and although neither gave us a sense through our fingers of how much work the front tires were doing to turn the car, neither one was unpredictable at speed. (Parking speeds produced the single most unnatural feeling.) We wish there were at least one test car available without variable ratio steering so we could have compared them. Yet at speeds that would (and did, for some) get the notice of the local constabulary, both cars felt planted yet eager without feeling heavy or darty. Turn in is crisp (a little crisper in the S5, thanks to the shorter wheelbase and wider track width) and authoritative through the friction-free wheel. We know part of this crouched-and-ready feeling has to do with the electronic rear differential in the S Sport package. Quick to respond, the torque-vectoring differential routes power to the outside wheel to help point it in, but more important, it puts the power down on exit. Mat the throttle on corner exit, and the car simply sticks and goes where the front wheels are pointed. There's no tail-out rally-style antics here. It's all steady and precise without a need for correction, tracking through corners felt almost like a nonevent. The positive spin says this allows a driver to pay attention to his or her chosen line or avoid a large stone or road kill—all of which we did. We even tried unsettling the cars mid-corner with deliberate, ham-footed jumps into and out of the throttle. The car merely displayed extremely mild understeer in off-throttle moments and utter neutrality on-throttle. "Smoove" seems to be a theme for these "S" cars.

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The Experience

The standard seats, optionally wrapped in Nappa leather, were coddling and appropriately firm. The side bolsters were effective without being intrusive. From inside either of the cars, the exhaust note was sporty and reedy but also somewhat muted and shy of what we'd call snarly. We'll assume raucous behavior will be reserved for the RS versions—the 2018 Audi RS5 made its debut recently in Geneva with a 2.9-liter twin-turbo V-6, but we haven't heard it yet. The S4/S5's multivalve dampers have distinct ride qualities between Dynamic and Comfort modes, and Automatic mode is so clever that it doesn't seem to get flummoxed by much of anything. It's also nice to have two ways to select driving modes: either from the MMI controller or, even more handily, cycling up or down through them with the toggle switches hanging off the dashboard. In Dynamic mode, road irregularities have sharp edges, and in Comfort they are handled in the classic one-and-done fashion without secondary body motions. Throttle, steering, and damping responses are all heightened in Dynamic mode, yet both cars remained composed, predictable, and ready in their max-attack modes.

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Like the previous supercharged V-6s, the new turbocharged engine's power delivery was remarkably linear. However, unlike the previous engine where torque peaked at 2,900 rpm and horsepower at 5,500 rpm, maximum torque is now produced from 1,370 up to 4,500 rpm. Horsepower now peaks at 6,400 rpm, giving the new engine an even broader driveabilty and longer legs. Quick as they might prove later in testing, the new S4/S5 quattros acceleration is not shocking and explosive the way the recent RS 3 was. They do, however, feel relentless all the way up to the indicated 6,500-rpm redline and beyond. Remember when turbos used to whoosh and hit hard? Instead, speed piles on in that sneaky "Whoops! I'm going 80?" sort of way. Although it doesn't have the aural qualities of the long-gone 4.2-liter V-8, this more powerful and more efficient turbo-six feels remarkably similar to that gem of a motor but without the bark or engine braking of the V-8.

The Competition

Starting at $51,875, the 2018 Audi S4 Premium Plus quattro (354-hp turbo V-6 and all-wheel drive) lands right between the current BMW 340i xDrive (320-hp turbo inline-six and all-wheel drive) and the Mercedes-AMG C43 4Matic (362-hp turbo V-6 and all-wheel drive). Undercutting them all is the Cadillac ATS-4 Premium Luxury (335-hp V-6 and all-wheel drive). In terms of straight-line performance, interior sophistication, driver engagement, and overall confidence, we'd say the Audi and Mercedes are pretty well matched. Even if it could manage to maintain pace on a twisty road, the BMW 340i feels older, heavier, and more ponderous. The Cadillac ATS certainly has a world-class chassis, but because it lacks a turbocharged engine, it would not likely rise to the occasion if that meant venturing to climes where the air gets thin. To make an objective choice, we'd really have to bring them all in for a proper comparison test.

With a nearly identical relationship in price, performance, and overall execution, at $55,575, the 2018 Audi S5 Premium Plus quattro again would find itself in the midst of a battle with a Mercedes-AMG C43 4Matic Coupe, to a lesser degree with a BMW 440i xDrive, and a Cadillac ATS-4 Coupe.

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What we can tell you is that both the 2018 Audi S4 and S5 quattros have added a new level of interior and exterior sophistication to what were already competent—if a little bland—cars in their previous iterations. We especially appreciate the S5's finer-line attention to surface detailing and the instantly recognizable hips and roofline. Check out how the hood's cutline is now hidden in the front fenders' character line. So cool. The new turbocharged engine is better in every measurable way from either the supercharged V-6 it replaces or the once-burly V-8 it outpaces. The new eight-speed automatic should not be dismissed out of hand. Its logic when left to its own devices is very good. There are few if any "C'mon already!" moments. The transmission responses in Dynamic mode—or when manually forced to swap cogs up or down the scale—are practically indistinguishable from most twin-clutch automated manuals. These two B9-era S variants are finally threatening the best in the class and perhaps have even set new benchmarks in several categories.

Audi is certainly cranking out some of the best-looking, best-equipped, and most-engaging hardware these days, and these two enthusiast-oriented (just shy of RS hardcore) examples prove Audi knows how to not only create consumer friendly sedans (A4, A5, and A6) and full-on sports cars (TT RS, RS 3, and R8 V10 Plus) but also how to also fill in the middle bits with these attractively priced, powered, and poised newcomers.