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Adam Davis17 Aug 2015
REVIEW

Turbo Twins: Mercedes-AMG GT S v Porsche 911 Turbo

AMG’s sexy new super coupe takes on Porsche’s sports car king
Models Tested
Mercedes-AMG GT S v Porsche 911 Turbo
Review Type
Comparison

Porsche’s 911, in its various iterations, has ruled the sports car roost for generations. From the straight-line supremacy of the Turbo to the raw dynamic purity of the GT3, there’s been little to touch the Stuttgart squad. So complete is Porsche’s superiority that Mercedes-AMG has yet to dip its toe into the series production sports car waters… until now. Enter the AMG GT S.

Indicator blinking, a fountain of dust spurts from the Porsche 911 Turbo’s 305-section rear tyres as it turns off the highway and heads for the Gippsland hills.

Following the 911’s lead, the Mercedes-AMG GT S blips a couple of down-changes into the cabin, priming that tremendous biturbo V8 for accelerative action.

In some ways it’s a shame to leave the highway in the GT S, for you deny others its incredible road presence. Where the grey Porsche almost blurs into the scenery – if you can catch it at all – the Mercedes-AMG, with its guttural exhaust and swooping exterior design which melds the best bits of 300SL Gullwing with sleek modernity, is literally jaw slackening.

Cockpit is an apt description of the AMG’s interior. It’s replete with roof-mounted switches and brushed metal details, but there’s no time to acknowledge that it’s more advanced than the Porsche in its packaging, with a usable glovebox, cup holders for your lattes and covered storage to go with the raised, metal-edged central console and gorgeous leather seats.

Instead, the dry-sump, 4.0-litre 375kW V8 responds with immediacy to the throttle, the two ‘hot inside-V’ turbochargers spooling quickly as the cabin is drenched in thunderous noise. A clever electronically-controlled locking differential forces 650Nm torque through the rear 295-section Michelin Pilot Super Sports with surprising traction…

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Who said turbos destroy sound? Or response?

Still, the 911 Turbo’s famous rump pulls away inexorably, overboost function adding 0.15bar (for a total of 1.15) and inflating the already-massive 660Nm torque slug to 710Nm, for up to 20sec. As if the twin-turbo 3.8-litre iteration of the flat-six and its 383kW at 6500rpm needed any help.

Over 5000rpm, the menace of the GT S curiously reduces in intensity, like it’s throttled back from where it could be. The last lunge to redline feels slightly strained – perhaps AMG is holding something back for a later Black Series power-up? So, you snap the right paddle, engage the next gear, and feel the full force of its torque once more.

Regrouping for photography gives an opportunity to catch a breath, before poring over the Porsche in more detail.

Despite a wheelbase stretch and wider tracks over the previous 997-generation 911 Turbo, the new car remains taut. There may have been accusations of bloatedness, but the 911 is still a small car -- at least until you scope those hips.

Inside this 991 version of the 911 Turbo is far more premium than its predecessor. Yet it still trails the Mercedes-AMG for comfort, usability and sheer sense of occasion. It does, however, have two rear seats. They may be occasional for adults, but are a great way to take the kids to school.

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Another key point to consider is pricing. There’s a $71,500 difference between the two, with the Mercedes-AMG GT S requiring $295,000 (plus on-road costs) to acquire. The Porsche, on the other hand, is a rather fulsome $366,500 in PDK form.

At this stage, the difference is hard to justify beyond the intangible ‘heritage’ angle, but the perceived value gap reduces once you come to terms with the Porsche’s otherworldly on-road ability.

Following the strip rear LED lighting of the AMG GT S, the 911 Turbo does a fine job of shrinking around you on the road and it turns-in with assurance, assisted by active rear-steer and an electrically-controlled all-wheel drive system that can shuffle 100 per cent of drive torque to the front or rear axles as required.

Active torque vectoring also plays its part, ensuring each corner’s grip/go ratio is maximised.

Over and above the Porsche’s extraordinary combination of raw grip, immense traction and the advanced technologies to harness it all, is the sheer quality of its body control. It is resolute. This 911’s damping response is refined to its unique weight balance and demonstrates a product that’s been honed over five decades.

The Porsche’s steering is also more natural in feel and progression through its thin-rimmed tiller, despite also being electrically-assisted.

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The rear-steering counter-steers to sharpen turn-in response at slower speeds but reverses to aid high-speed stability. That said, there remains a little of that lightness just off-centre that reminds you of the engine’s unique position. Braking, of course, is impregnable -- once you’ve worked some heat into the discs’ surfaces.

In concert with the Porsche’s dynamic repertoire is that towering engine. Responsive, torquey and far-reaching, the 911 Turbo driver can easily keep pace with the AMG on the varied, bumpy, off-camber roads we used for our drive. Simply pick the normal chassis setting and sport plus engine mode for all-road, all-weather excellence.

What about the transmission? The PDK is quick-shifting and positive, but even when switched to what should be full manual mode, the gearbox will kick down if the throttle détente is pushed past.

This is an unnecessary blight on the 911 Turbo’s copybook, given its immense mid-range is more than capable of running a gear – or two – higher. Simply, it doesn’t need to be straining at high revs for maximum thrust, and the kick-down can upset the 911’s mid-corner balance.

Swapping once more into the AMG, its comfort suspension mode rides nicely but lacks control, apparently bobbing slightly over bumps before resettling. Shift into sport suspension mode and the control comes, but the ride response switches to a sharpness that is also felt via hyper-alert steering.

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You have to recalibrate your brain to this instantaneous response, smoothing your input and knowing the front-end will respond in kind. From there, the GT S shows off its throttle adjustability, its rear-end pivoting to the pressure from your right foot before hunkering down to make most of the inherent traction the AMG’s transaxle layout provides.

Throw in that clever differential, which can open or progressively lock on-demand, and the GT S bites hard on corner exit. The only histrionics emanate from the exhaust.

The ‘diff’ system even aids stability under braking, which is prodigious in its own right even without the carbon-ceramic option box ticked.

On these roads the AMG is best left out of sport plus for its suspension, which makes the ride thoroughly crashy and is therefore a smooth circuit setting. The engine, however, thrives on sport plus, and it’s practically essential to employ same for the rampant exhaust. Manual mode for the transmission is, refreshingly, fully manual, giving the driver another layer of control, as well as perfect paddle shifts.

But still the Porsche is the more complete when seeking back road solace.

The above isn’t a criticism of the Mercedes-AMG, however. In its first real foray into the 911-rivalling market, Affalterbach has created a formidable adversary. The thought that the GT S is a baseline glimpse of what a GT Black Series could offer enthusiasts is tantalising.

As it stands, GT S versus 911 Turbo, the Porsche still stands out… But not by much. Swap Turbo for Carrera S or even GTS and the balance could well skew Mercedes-AMG’s way.


Price: $295,000 (plus on-road costs)
Engine: 4.0-litre twin-turbocharged V8 petrol
Output: 375kW/650Nm
Transmission: Seven-speed dual-clutch
Fuel: 9.4L/100km (ADR Combined)
CO2: 219g/km (ADR Combined)
Safety: Not yet tested

What we liked:
>> Jaw-dropping presence
>> Animalistic engine sound
>> Chassis grip…

Not so much:
>> … once you’re used to the hyper-alert steering
>> Floaty body control in comfort mode

2015 Porsche 911 Turbo pricing and specification:
Price:
$366,500 (plus on-road costs)
Engine: 3.8-litre twin-turbocharged flat-six petrol
Output: 383kW/660Nm
Transmission: Seven-speed dual-clutch
Fuel: 9.7L/100km (ADR Combined)
CO2: 227g/km (ADR Combined)
Safety: Not yet tested

What we liked:
>> Damping refinement
>> Stonking engine performance
>> Incredible traction

Not so much:
>> PDK will still kick down in manual mode
>> Price gap

Performance:

(Note, ‘fast road’ start, transmissions in drive, no ‘stalling up’)

Mercedes-AMG GT S Porsche 911 Turbo
0-60km/h 2.7sec 2.0sec
0-100km/h 4.5sec 3.6sec
50-70km/h 0.9sec 0.6sec
80-100km/h 0.9sec 0.9sec
0-400m 12.39sec at 197km/h 11.56sec at 202km/h
dB(A) at 80km/h 82 80
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Written byAdam Davis
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