Audi's (slightly) nastier looking new coupe has gained 0.6 inches of width and wheelbase and 2.9 inches of length but lost 132 pounds of mass along the way. Even better, the smaller 2.9-liter twin-turbo V6—the same one found in the Porsche Panamera—produces the same 450 horsepower as before, but gains a thumping 125 lb-ft of torque over the old V8, bringing the grand total of twist to 442 lb-ft. As with the previous RS5 you can't get a manual, but this time Audi swaps their signature dual-clutch transmission with an 8-speed torque converter unit from ZF. The reasoning is sound: the DSG 'box couldn't handle the engine's output, which produces more torque than the R8's mighty V10 – #bigtwistproblems.

The RS5's weight loss stems from strategic use of aluminum and the loss of the stonking V8 (ditching it for the twin-turbo V6 saved 68 pounds alone). Weight distribution is, of course, also aided by the lighter front end, and the rear trapezoidal suspension setup has been supplanted with a five-link arrangement for smoother ride and sharper handling. Interior space also benefits from the larger footprint, with rear seat legroom benefiting most from the roomier dimensions.

The roads from Toulouse, France to the tiny principality of Andorra offer contrasting extremes, from arrow-straight superslab to ultra-technical twisties – an excellent test of the RS5's performance repertoire. The updated cabin presents Audi's typically understated style, with available honeycomb top-stitched leather seats that are supportive but not so tight as to be constricting. HVAC slats form a continuous extension across the dashboard (a la Q7), and the steering wheel and shifter can be trimmed in either perforated leather or Alcantara.

The first thing you'll notice in the RS5 are the low frequency sounds, which round out the otherwise muted engine noises. Aided by a passive shaker on a metal flap that resonates the windscreen, those nearly subsonic booms and bellows are complemented in sport exhaust-equipped cars with an exhaust valve that comes alive during aggressive driving (or when the system is switched to its sportier setting). The sound isn't nearly as raucous as the V8's warble and some might feel it's too quiet. Then again, however pleasant the engine's subtle bass line is, after a bit of spirited driving you might prefer the system to be switched to normal mode so you can hear your own thoughts.

The second thing to hit you is the turbo motor's tremendous torque. The plateau starts at 1,900 rpm and doesn't drop off until 5,000 rpm; Keep the throttle buried, and the engine continues to pull strongly until peak horsepower is reached at 6,700 rpm. Though it takes a moment for boost to build at low rpm, there's a potent rush of power once the hot-vee turbos kick in that quickly shoots the digital tachometer towards redline. When equipped with the optional virtual cockpit, the display flashes yellow then red, escalating as redline is approached. Incidentally, the visible warning is one of several RS-specific indicators which include engine output, tire pressure and temperature, and g-forces. With a zero to 60 mph time of 3.7 seconds, that gearchange mambo occurs impressively fast, and the RS5 launches forward forcefully.

Thanks to a new hydraulically linked shock setup with cockpit adjustable damping, the RS5 felt markedly different depending on which mode was selected. In comfort, the ride is still somewhat firm but moderately sized potholes are filtered out. Select sport and it stiffens up to a point that you wouldn't want it on a bumpy road; marble smooth tarmac is manageable, but you'll get diminishing returns in the stiffest setting on most real world surfaces.

Though the ZF 8-speed is a tad jerky even its mildest settings, the speed of the upshifts and rev-matched downshifts do not disappoint—if anything, the gearbox seems to work better when the car is driven hard, offering an effective way to transfer power to all four wheels. The default power split is 40/60 through the Torsen differential, with up to 85 percent driven to the rear or 65 percent to the front. Opt for the sport differential feature, and power is managed at the rear using a mechanical vectoring system via two clutches. Additionally, brake vectoring is used at all four wheels to help rotate the car in corners.

On the impossibly tight switchbacks through the steep ascents of the Pyrenees mountains, the RS5 felt taut and responsive. Sure, there's a bit of the requisite understeer at corner entry, but the grip levels are high enough to encourage seriously high speeds. The RS5's linked hydraulic shock system, first seen on the RS7, offers the effect of a virtual anti-roll bar by enhancing body control as the car negotiates a corner, and the feeling is reassuringly glued-down. Perhaps even more impressive are the optional ceramic front brakes, part of the Dynamic plus package. The stoppers feature massive 400mm rotors – larger than the R8's – and never felt overtaxed despite plenty of sudden decelerations.

While the new Audi RS5 introduces a number of practical improvements, among them more space and 17 percent better fuel economy, the most significant upgrades are undoubtedly its lighter weight, refined chassis, more variable suspension, and considerable boosts in engine output. "You buy horsepower," says Audi Sport development head Stephan Reil, "but you drive torque," a sentiment that rang true as I dipped into the RS5's irresistible powerband while tackling some supremely twisted roads.

Since some of the RS5's strongest competition has embraced turbocharging to great effect—particularly the Mercedes-AMG C63 Coupe and BMW M4 – we can hardly blame Audi for making the switch. Lighter, stronger, and nimbler than before, the new RS5 goes and turns like stink yet stands apart from the Benz and Bimmer crowd. At last, the RS5 doesn't feel like it sacrifices performance for its individuality within the hot rod coupé microcosm. In our eye that's a huge win, and an excellent bellwether for the expanding Audi Sport lineup.