The Mercedes-AMG GT63 S 4-Door is the fastest and most powerful AMG you can presently buy. Does it live up to those promises?

When the AMG GT63 is finally let off the leash, it leaps forward with such stunning aggression that not only does it startle driver and passenger, but the mountain of torque shocks the rear differential and breaks the Michelins’ hold on the cold tarmac. For the hour prior, the 470kW, 900Nm AMG had lulled us with its limousine credentials, cosseting us through Melbourne’s late peak-hour traffic with a surprisingly relaxed gait and an interior that almost rivals that of an S-Class for luxury.

We’re now very familiar with Mercedes-AMG’s prolific and characterful twin-turbocharged 4.0-litre V8, but never before has it thundered out more power. With 470kW, the GT63 S 4-Door is the most powerful AMG that you can presently buy and is only outmuscled by a handful that have gone before it – think ultra-rare models such as the twin-turbocharged V12-powered SL65 Black Series and SLS Electric Drive.

For now, at least, this is the ultimate iteration of the brand’s M178 engine and the 470kW summit is available from 5500-6500rpm. There’s also a 900Nm table top of torque from 2500-4500rpm. These are truly huge numbers and it wasn’t very long ago that no supercar in the world could muster such figures. Consider also that by taking just 3.2 seconds to reach the out-dated benchmark, the AMG GT63 S 4-Door can match a McLaren F1 to 100km/h. At 2045kg, the AMG is more than 900kg heavier than the three-seat superstar.

It’s hard to tell whether a 0-100km/h benchmark has more or less relevance than a Nurburgring lap time, but at least the latter proves a level of dynamic competence. Having cut a 7:25.41 around the Green Hell, the GT63 S lays claim to the title of world’s fastest four-door and heightens our expectations when the roads of the model’s Victorian launch venue turn interesting.

Thankfully, the thundering V8 is not another dull-sounding, dead-feeling high-boost turbocharged engine. Like most AMG engines, it brims with aural character and, despite a static compression ratio of just 8.6:1, it has sharp throttle response and certainly never feels tardy to spool-up. The off-idle throttle tip-in is keen but not abrupt, and the low-rev eagerness is matched by the ferocity with which the engine storms to its 7000rpm redline. In fact, like all M178s, the application in the GT63 S requires attentiveness in order not to stumble into the rev limiter. I fail the test only once when I am fixated on the horizon rushing up over the bonnet and in through the windscreen, missing my chance to grab fourth in time.

While 900Nm would cover most situations with just a brace of ratios, this mighty M178 is backed by a nine-speed MCT gearbox. Thankfully, the ratios are pretty sensible with first, second and third gears running to 54, 90 and 130km/h respectively. Sixth gear is direct, leaving the top three cogs as overdriven ratios. Incidentally, the GT63’s 315km/h top speed is achieved in seventh gear at 6500rpm.

Ultimately the gearbox isn’t as smooth at the slow and boring stuff as the ubiquitous ZF eight-speed torque converter auto, nor is it quite as crisp and sharp as a Porsche dual-clutch unit when the going gets fun, but it does a fine job at both ends of the gear-shifting spectrum.

Tasked with controlling and delivering the V8’s vast outputs is Mercedes’ 4Matic all-wheel-drive system. It’s an active system that is constantly altering drive front to rear but in normal, high-grip situations the GT63 S is largely rear drive. Dial in Drift Mode, and like the E63 S, the big GT is purely two-turning, two-burning.

After the GT S and current-generation CLS, the GT 4-Door – range-topping 63 S featured here and the upcoming 53 – is the just the third model developed entirely in-house by AMG, rather than the usual practice of Mercedes-Benz leading the model development and AMG fettling to their needs. Unlike the bespoke GT S architecture, the CLS and now the GT 4-Door are underpinned by Mercedes’ MRA platform that also forms the basis of the E-Class.

And this is where it is easy to be cynical and suggest that the GT63 S 4-Door is just a fancy, and significantly more expensive, E63 S. After all, they share the same fundamental chassis and drivetrain, and the 450kW, 850Nm E63 S is hardly slow and it will save you nearly $110,000 over the $349,900 GT63 S. In Mercedes-AMG’s defence, there are significant engineering differences between the body-in-white of the two models. Firstly, the GT63 sits on a wheelbase stretched 12mm to 2951mm, and its total length of 5054mm is 65mm longer than an E63 sedan. Beyond that, the structure of the GT63 S is vastly different and stronger than that of its little brother. Up front, there’s an alloy plate under the engine that helps stiffen the front structure, then there are three cross-braces to strengthen the transmission tunnel, with a further two beams that run diagonally from the trailing edges of the sills to the boot floor. Finally, the rear structure is stiffened by more bracing in and under the boot, and a carbonfibre bulkhead behind the rear seats.

From this very stiff structure, Mercedes-AMG’s engineers have hung a four-link front suspension, with a five-link at the rear. Multi-chamber air springs feature at both ends, with twin-tube dampers up front and single-tube shocks at the rear. The whole set-up is over seen by the adjustable AMG Ride Control system.

In light of the five-metre length and that three-metre wheelbase, it’s a good thing that AMG has included a rear-wheel-steering system that aims to improve agility at low speeds and stability at high speeds.

Back to that first hit of torque and what was meant to be a simple overtaking manoeuvre quickly escalated to the kind of speeds that have you locked up and your car crashed by gleeful do-gooders. Given the spec run-down you’ve just waded through, it wouldn’t be much of a surprise that the new AMG is fast, but when you’re sat in the passenger seat, happily chatting to a colleague, another four-letter F-word immediately springs to your lips.

My turn behind the flat-bottomed steering wheel confirmed the new AMG’s outrageous pace, but also its depth of character. Initially, however, I couldn’t quite gel with the big sledgehammer. I felt as though I was always reacting to the car, rather than it doing my bidding. I also couldn’t get the standard Michelin Pilot Sport tyres (275/35 ZR21 and 315/30 ZR21) to key into the sometimes dry, sometimes damp coarse-chip surface. Instead, it felt as though the GT63 was tip toeing down the road, slipping here and there from both ends. Add in the sheer size and weight of the AMG and it wasn’t a car to hustle from the off.

Instead, I relaxed my inputs and expectations and let the car come to me and the conditions. Gradually, the pace crept up and the GT began to sparkle.

It’s important to settle the nose before corner entry in order to banish any hint of understeer. This isn’t to imply that it’s merely a point-and-shoot weapon, just that you need weight over the nose before you begin asking the hard questions. Thankfully, the steering provides enough feedback so that you’re not second guessing the onset of understeer, in fact, there’s always a level of feedback upon which you can draw.

A tight and sometimes damp public road is no place to fly solo with a 470kW, 900Nm, two-tonne limo, but the chassis delivers enough feedback that it feels somewhat sensible to relax the stability control to sports handling mode. Instead of clamping down on any exuberance, this setting gives you the latitude to float the car along and settle any minor disputes yourself. ESC remains in the background, ready to help remedy bigger indiscretions with a swift but not too firm hand.

Get into a rhythm with the big GT over a series of corners and you can begin to sense the rear-wheel steering come into play. It all seems to click and the car begins to shrink and transition through changes of direction like a much smaller car. It’d be a stretch to suggest that it feels like a C63, but it’s not far off.

A small word of caution, however. Even once you’re in tune with the GT63 S, it remains a challenging and engaging car on a fast downhill run, as the big rear end wants to play on corner entry. Perhaps it’s just the world’s largest hot hatch and it wants to lift-off oversteer like a Peugeot 205 GTi. Again, the steering comes into its own in such circumstances and if you open the angle by a few degrees you can diffuse the situation by taking some of the tension out of the dynamic load.

Later, I have the opportunity to test the blue car pictured and its optional Michelin Pilot Cup 2s make a world of difference. The Cups deliver a square-shouldered confidence to the turn-in phase and enough grip to encourage early explorations of throttle travel as you first sight the exit. The AMG can still overwhelm the sticky rubber, but it happens less frequently and with more clarity.

The standard brake package features 360mm rotors at both ends, the fronts squeezed by six-piston calipers with single-pistons at the rear. Both examples that we tested were fitted with the optional carbon-ceramic rotors (402mm front and 360mm rear) clamped by six- and single-piston calipers front and rear, respectively. The optional brakes never hinted at going long or grumbling and managed the weight and speed of the GT63 S with relative ease.

When uncorked, the engine really is something extraordinary, chewing through revs and ratios with disdain. Though its mid-range obviously swells with turbocharged torque, the delivery is such that it doesn’t quite drop your stomach like a McLaren 720S, Porsche 911 GT2 RS or other similarly powerful cars. But that we even dare to compare the GT63 S 4-Door with some of the very fastest cars this magazine has ever driven says plenty about its outright pace and the ferocity of its engine. Every now and again, there was just the slightest hesitation to granting a shift request via the steering wheel paddles, but otherwise the gearbox and V8 are happily married.

The range-topping GT63 S 4-Door starts at $349,900, which places it exactly $100K over the $249,900 E53 GT 4-Door. While deliveries of the GT63 S have already begun, GT53 customers will need to wait a few weeks longer, but Mercedes-Benz Australia expects that the bulk of customers will be ordering the big boy. We’re keen to sample the GT53 as its mild-hybrid drivetrain combines a 320kW, 520Nm turbocharged 3.0-litre in-line six with an electric motor that is attached to the engine’s flywheel and acts as the starter motor and generator. The electric motor adds just 16kW but a rather more useful 250Nm. The 4Matic GT53 hits 100km/h in a claimed 4.5 seconds and tops out at 285km/h.

As is always the case at this end of town, there are numerous options that can quickly inflate the price of the GT63 S. One that we expect will be extremely popular is the $9500 exterior carbonfibre package that includes the front splitter, rear diffuser and side sill inserts. The car pictured features the aerodynamics package that replaces the automatic rear wing with a fixed element. With a gloss black finish, this will set you back $7300 or $11,600 in carbon (known as the carbon II package). The blue car pictured had the box ticked for Michelin Pilot Cup 2 tyres ($1600), carbon-ceramic brakes ($12,500) and the luxury rear package ($4600) that converts the three-seat rear to a two-seat, business class experience.

At this stage, M-B Australia has no plans to offer the non-S GT63 or the entry-level GT43 that are available in some overseas markets.

Having spent a few hundred kilometres merely scratching the surface of the GT63 S 4-Door, has my cynicism of the model melted away? The short answer is an immediate and emphatic yes. The longer answer is that the GT63 S feels like such a sophisticated product, bristling with speed and technology, that you need extended wheel time in which to really bond and explore its limits and personality. As it stands, I can confidently say that it sits apart from an E63 S and manages to carve its own niche in an increasingly fragmented model line-up and market place. And that is no mean feat. Jesse Taylor

Mercedes-AMG GT63 S 4-Door
Engine 3982cc V8, twin-turbocharged
Power 470kW @ 5500-6500rpm
Torque 900Nm @ 2500-4500rpm
Weight 2045kg (230kW/tonne)
0-100km/h 3.2sec
Top speed 315km/h
Basic price $349,900