Why does the new Mercedes-AMG GT63 S exist? Because the company's E63 S sedan—which hits 60 mph in 2.9 seconds, eviscerates the quarter-mile in 11 seconds flat, and laps the Nürburgring in the low 7-minute-and-40-second range—isn't quick enough. That's why.

And since Mercedes-AMG is a company filled with formally dressed, stern and stoic Germans, you'll believe them when they tell you that the GT 4-Door's chassis is stiffer than the E63's, that it can better support higher cornering loads from its wider tires, and that all this is necessary to undergird the highest-output version of the company's twin-turbocharged 4.0-liter V-8 produced to date, which is housed under its hood. Yet when all 630 of the GT63 S's snarling horses are loosed, you'll understand that the Affalterbach cowboys' austerity is only a veneer spread thinly over their true lunatic temperament and that their Dressler suits are merely a façade worn over John Force Underoos.

The GT63 S, after all, comes standard with a drift mode.

This latest AMG creation is so potent, in fact, that those same cowboys felt it necessary to limit the cars we drove on roads around Austin, Texas, to 100 mph, disable drift mode, and permanently enable stability control. Possibly they know us as well as we know them. The GT63 S is so fast that when the electronic reins began to draw tight at about 90 mph—to keep us from pulverizing the 100-mph limit—we'd been in the throttle for only about four seconds. So we believe AMG CEO Tobias Moers when he tells us that the GT63 S will lap the 'Ring in the 7-minute-20-second range. And even though those same stoic Germans call the car a four-door coupe, we'll save ourselves the time and words. This is a sedan. A ridiculously rapid one.

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The Build of a Beast

Three variants are available: the track-slapping GT63 S described above; the 577-hp GT63, which uses a slightly less mad version of same 4.0-liter V-8; and the GT53, which employs the brand's new 3.0-liter inline-six good for 429 horsepower thanks to a turbocharger, an electric supercharger, an AC motor, and a 48-volt electrical subsystem. A GT43 model, with 362 horsepower from that inline-six, is available in other markets but won't be sold here initially. A word about the GT63 S's engine: Its additional power beyond the 603-hp version in the E63 S comes courtesy of twin-scroll ball-bearing turbos—the E's engine uses journal-bearing turbos—and a reworked engine calibration. All GT 4-Doors come with a nine-speed automatic; the GT53's transmission uses a conventional torque converter, while V-8–powered cars ditch the fluid coupling for a multiplate clutch pack. 4Matic all-wheel drive is standard across the line.

Speaking of all-wheel drive, here's a cool trick: Toggle the GT63 S into Race mode, wood the brake, pin the throttle, and smirk smugly as the tach needle stalls in a nervous twitch halfway around its sweep. Enjoy the fireworks show on the instrument panel as the boost gauge, tachometer, oil pressure, and other meters dance in unison. Then lift your left foot and let the GT's 4Matic system vaporize any ideas you might have had about all-wheel drive not pulling its weight. It's possible we felt the skin on our face stretch tightly into Elvis lips as we attempted to smile through the g loading.

Although its more svelte styling might lead you to believe this is a smaller car than the E-class on which it is based, the truth is that its wheelbase, at 116.2 inches, is 0.5 inch longer than an E63 S sedan's, and its length is 2.8 inches greater as well. (The GT 4-Door is actually based on the chassis of the E63 S wagon, which has the same wheelbase as the sedan.) Being 1.8 inches wider than the E63 S make its overall proportions more aggressive and helps accommodate slightly wider rubber. Numerous steel and aluminum braces beef up the GT 4-Door's body, many of which aren't present on the E63 S. There's an aluminum shear plate under the engine as well as three braces spanning the center tunnel. A carbon-fiber trunk floor helps shave weight.

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AMG let us drive the GT63 S on the Circuit of the Americas track, where the big sedan—Moers says it weighs about the same as an E63 S, a touch under 4600 pounds—proved itself highly capable wearing the Michelin Pilot Sport 4S rubber that comes standard. Pilot Sport Cup 2 track tires are optional, but AMG representatives tell us most buyers don't opt for them on other models. What we can say for sure about the GT is that it's the most approachable big sedan we've ever driven on a racetrack, resolutely following steering commands like a car two-thirds its size and weight. Some measure of this obedience is due to its rear-axle steering, which is standard on the V-8 models and endows the car with rotational abilities not unlike the smaller, lighter AMG GT R. By shifting some of the steering load to the rear, the heavy GT 4-Door turns with far greater confidence than most of its competitors.

Confounding Complexity

There's also an electronically controlled limited-slip rear differential that the GT 4-Door shares with the E63 S. The diff, rear-axle steering, stability control, and all-wheel-drive system work together under the authority of the AMG Dynamics system, which is new with the GT 4-Door. Four levels of AMG Dynamics—Basic, Advanced, Pro, and Master—scale upward in aggression with five of the six Dynamic Select driving modes (Slippery, Comfort, Sport, Sport+, Race, and Individual), which are switched via a steering-wheel-mounted knob or by using a toggle on the center console. The driving modes control the sharpness of the engine and transmission responses as well as the weight and effectiveness of the steering, suspension damping, and active exhaust settings. Air springs are standard on V-8 models and change ride height with the driving modes, while six-cylinder GTs come with steel coil springs.

The point of the AMG Dynamics system, according to AMG test engineer Kevin Berger, is greater individualization. In practice, however, it's a lot of complexity. This is what happens when one car tries to be everything to everyone. And we're not faulting the GT 4-Door's abilities—it certainly offers a high degree of track ability mixed with relatively benign everyday comfort, even on huge wheels and ultra-low-profile tires. But learning which AMG Dynamics modes correspond to which Dynamic Select modes and then sorting out how to best configure it all to suit your favorite Individual mode will require biological-evolution levels of experimentation. It's not a car for the uncommitted.

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Iron brake rotors are standard on all GT 4-Door models, and carbon-ceramic rotors—which save 35 pounds—are optional. Fixed six-piston front calipers and single-piston sliding rear calipers are fitted with both types of rotors. Eleven wheel options, ranging from 19 to 21 inches, are available. Twenty-inchers are standard on GT63 S models, while the GT63 and GT53 come standard with 19s.



Luxurious Digs

Look inside and you'd never know the crafty loons at Affalterbach were involved. The GT 4-Door's cabin is a gem, and although its interior trim is highly configurable depending on your taste and budget, every model we drove was a stunning combination of wood, leather, microsuede, and carbon fiber. Similar to the E-class, two high-resolution 12.3-inch TFT displays make up the instrument cluster and infotainment screen. In addition to the one for the driving modes, toggle buttons controlling the transmission mode, suspension damping, stability control, wing position, and exhaust mode are found on the center console.

Optional front seats with more lateral bolstering and a fixed headrest are available. The standard rear-seat configuration consists of two fixed-back seats supported by a carbon-fiber shear panel, which adds stiffness to the chassis. The Executive Rear Seat package does away with the carbon-fiber panel in exchange for folding seatbacks and a larger console between them with a touchscreen to manage the rear climate controls, lighting, and seat heating. Space in the rear seats is adequate for six-footers, but just barely. And there's no way any of the Affalterbach cowboys is going to squeeze a Stetson back there.

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Mercedes says the GT63 S will hit 60 mph in 3.1 seconds, but we've already shown that the E63 S, which weighs the same and makes less power, can devour that milestone in only 2.9 seconds, so that appears to be an understated claim. We haven't yet strapped our test gear to the GT63 S, but we can say that from a standstill it's easily as rapid—and maybe more so—than any of its competition. Among four-doors, only Porsche's electrified (and 700-pound-heavier) Panamera Turbo S E-Hybrid and the grip-limited, rear-wheel-drive Cadillac CTS-V have more power.

But we know, based on conversations with those tricky Germans, that this is much more than just an acceleration game. They want the GT 4-Door, in every form, to be a comprehensively capable car, one that gives up nothing in comfort, performance, and attitude. By all appearances, and provided you're willing to spend some time dialing it in, it seems they've succeeded.

Pricing isn't announced yet, but at about $140,000 the GT63 would undercut the Porsche Panamera Turbo by about 10 grand. GT 4-Doors will be in dealers in early 2019, which gives the Affalterbach boys enough time to do a few more covert powerslides and hang another John Force poster on the wall before slipping into their Guccis to roll out their next creation. But it doesn't matter anymore. We know their secret.

Specifications Specifications VEHICLE TYPE: front-engine, all-wheel-drive, 4-passenger, 4-door hatchback

ESTIMATED BASE PRICES:

GT53, $115,000;

GT63, $140,000;

GT63 S, $155,000 ENGINE TYPES: turbocharged, supercharged, and intercooled DOHC 24-valve 3.0-liter inline-6, 429 hp, 384 lb-ft + AC motor, 21 hp, 184 lb-ft (combined output, 429 hp; 1.0-kWh battery); twin-turbocharged and intercooled DOHC 32-valve 4.0-liter V-8, 577 or 630 hp, 590 or 664 lb-ft TRANSMISSION: 9-speed automatic with manual shifting mode DIMENSIONS

Wheelbase: 116.2 in

Length: 199.2 in

Width: 76.9 in

Height: 56.8–57.3 in

Curb weight (C/D est): 4350–4600 lb PERFORMANCE (C/D EST)

Zero to 60 mph: 2.9–4.2 sec

Zero to 100 mph: 6.6–9.5 sec

Standing ¼-mile: 10.8–12.4 sec

Top speed: 174–195 mph EPA FUEL ECONOMY (C/D EST)

Combined/city/highway: 16–24/14–22/21–28 mpg Expand Collapse

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