Mercedes-AMG GTS vs Porsche 911 GTS (2015) review

Published: 09 February 2015

► Twin test: Merc AMG GT vs Porsche 911
► World-first GT S vs GTS comparison
► Has the 911 finally met its match?

No matter how hard anybody tries to usurp the perennial 911, Porsche always seems to have an answer. On the day we at last drive Mercedes’ spanking new V8-engined GT coupe with its box-fresh GTS badge, Porsche brings along a new kind of 911 with exactly the same moniker: 911 GTS. Sorry Mercedes, but nobody ever said this was going to be easy. 

The AMG GTS is one mega Merc, though – the baddest Benz there’s ever been. It’s even meaner than last year’s SLS Black and much more awesome than the crazily expensive yet underwhelming SLR co-developed with McLaren. The 508bhp AMG GTS, which easily beats the 628bhp SL65 AMG against the stopwatch, will be launched early next year together with a less expensive base version rated at 460bhp. The 911 has rarely faced a more serious threat.

The 424bhp flat-six-powered 911 GTS fuses elements of the GT3 batmobile with the DNA of the Carrera S – flared arches, numerous performance-oriented details, go-faster cabin treatment and all. It’s the closest in concept to this Mercedes – the GT3 being way too compromised and the Turbo packing 4wd and a huge pricetag. If the game is Grand Tourer meets sports car, this is the final. 

Mercedes GT vs Porsche 911: our playground is the Alps

We’re in the Austrian Alps, where the AMG announces itself with a shout, both visually and acoustically. Its angry part-throttle exhaust rumble makes heads swivel, and the V8’s typical flat-out wah-wah reaches your ears long before the car comes into sight. It sounds equally throaty from inside the cockpit, which has largely been inherited from the outgoing SLS. The passenger cell is accordingly short and wide, rear three-quarter visibility is compromised, the upright position behind the wheel is defined by the towering instrument panel, the extra-wide transmission tunnel and the too-close-for-comfort rear firewall. This imposing driver environment is garnished with a spectacular battery of round air vents, a high-definition in-dash colour monitor, a pricey blend of optional soft leathers and matte carbonfibre inlays, and a centre stack loaded with buttons, knobs, switches and the stubby joystick gear selector. It’s a stage set for stardom, but it falls short in terms of legroom, airiness (even with the optional panoramic roof) and all-round visibility.

To a bystander, the 911 GTS is simply yet another 911. In reality, however, the latest widebody iteration wants to be the sportiest model this side of the super-potent halo specials. To stress the GT3 connection, it comes with bespoke black 20in wheels, blacked out bi-xenons, selected aero kit elements, low-drag mirrors, a made-to-measure rear apron, four black tailpipes and two lines of solid black badging on the bumper below the adjustable tail rudder. Inside, we find snug-fitting sports seats, an Alcantara-wrapped helm as well as special GTS cues like new instrument graphics and tasty charcoal aluminium trim. What you instantly notice in contrast to the AMG is the more spacious cabin, the token rear seats (a delete option), and the Porsche’s more compact dimensions.

On the lightly trafficked Munich-Lindau autobahn leading to the Austrian/Swiss border, the low-slung AMG GTS is the undisputed king of the fast lane, despite its 194mph limiter. You can feel the kick of the explosive twin-turbo V8, which packs the seven-speed dual-clutch transaxle transmission with a massive 479lb ft – on tap between 1750 and 4750rpm – and the mid-range acceleration is incredible. Treat yourself to the full urge of the 4.0-litre engine by revving it through the gears all the way to the 7200rpm redline, and you’ll go from 60 to 125mph in a hand-stopped 8.0sec – that’s the kind of stuff goose pimples are crafted by. The 911 takes 1.8sec longer. When the imaginary starting flag drops, the red car will storm from 0-62mph in 4.0sec and from 0-125mph in 13.8. Again with all the stops pulled out, the blue car does the job in 3.8 and 12.5sec respectively.

The 911 GTS whips up an extra 30bhp over the Carrera S, but it only does so above 6300rpm when a vacuum flap opens the second intake tract. Although the maximum torque is an unchanged 325lb ft, it now takes 5750rpm instead of 5600 to manifest itself. Peak power of 428bhp arrives at 7500rpm, which compares to 400bhp at 7400rpm for the Carrera S. In response to the bigger lungs, the GTS redline is lifted from 7400 to 7800rpm. Owing to less favourable aerodynamics, the rolling resistance of the wider tyres and extra weight, the GTS is only 0.1sec faster off the mark than the Carrera 2. So, is it worth an extra £7.5k over its barely slower sibling? The answer is an emphatic yes. On the motorway it’s exactly that mix of higher revs and later upshifts which keeps the 911 in the slipstream of the AMG. Since you carry more torque through the gears, there is more momentum and pushing power to play with. At the end of the long straight leading down to Lake Constance, the Porsche tops an unrestricted 191mph. It is thus almost as fast as the Merc, but it takes quantifiably longer to squeeze out the final 15 to 20mph.

A more grown-up kinda 911

There were times when more speed was the last thing the driver of a 911 would be interested in. Earlier generations were notorious for snap oversteer, susceptibility to crosswinds and tramlining, but over time r&d has exorcised most of these vices by advancing suspension development, improving aerodynamic stability and distributing axle loads more evenly. As a result, the 2015 911 GTS won’t bite back.

We know from experience that the 911 and the AMG GTS excel on the race track. Both cars have honed the dialogue between input and response to perfection, both are wonderfully intuitive. On a cordoned-off circuit, the Porsche begs you to hit Sport Plus which firms up the dampers, tops up the gearbox with adrenalin and puts the black box on alert. Not available in the 911 is an equivalent to the Merc’s Dynamic Select feature which invites you to choose from four different personalities when tweaking steering, throttle response, ride comfort, transmission strategy, engine sound and stability control. 

A classic CAR magazine twin test: we're first to pit Mercedes-AMG GT against Porsche 911 GTS (photography by Tom Salt)

Before heading for the mountains, we stop for the twin reality checks of petrol and car wash. The latter is easier said than done in the case of the AMG GTS – it’s 1939mm wide with mirrors folded, eclipsing the Porsche by 87mm. As for fuel, the real-life mpg is the usual anti-climax: over 504miles, the Merc averaged 18.7mpg, the Porsche 20.3mpg – the reverse of official figures. 

The northern climb to the Silvretta dam and summit (2037m above sea level) favours the Porsche. It begins with a series of about two dozen first-gear switchbacks, then, as it gains elevation, the road expands its radii bend-by-bend. Above the tree line, the landscape opens up and the corners form more self-conscious arcs. The terrain is still tricky though because even in the dry the glassy, low-grip surface encourages early understeer and late oversteer almost to the same effect as a thin coating of freshly fallen snow. The approach from the south is better suited for the bigger, brawnier AMG GTS. You can see for miles, and with the exception of a few hairpins near the top, most direction changes will happily accept third or even fourth gear.

With ESP in Handling mode, the AMG is virtually invincible on the fastest stretches of this panoramic spiral staircase to the sky. Laying down the full grunt can be a momentary struggle through first- and second-gear kinks, but once it pulls away on a longer leash the Mercedes will lick up the road like a hungry lizard darting left-right, right-left on its unerring suction-cup paws. The 47:53% weight distribution, the electronic diff lock, the ground-hugging centre of gravity, and the aluminium double-wishbone suspension make the car feel agile and alert, involving and inspiring. You want to be in Sport Plus on demanding turf like this, especially as the initially rather light steering now feels firm and meaty.

The 911 can’t pull off quite as many dynamic tricks. It also commands a surcharge for goodies like variable-effort steering, sports suspension and dynamic chassis control (PDCC). Although the 911 runs on even wider footwear than the AMG GTS, it actually rides better on these lumpy off-camber twisties that throw in crumbling shoulders and ancient repair patches for good measure. Thanks to the bespoke suspension setting, the fatter tyres and the wider track, this Porsche turns in with even more vigour as the front end will stick-stick-stick all the way through the corner. At the same time, the rear end carves round in g-force-defying follow-me fashion until ESP eventually calls time.

Who would have thought that, when maxxed out to the driver’s limit, the AMG is more challenging, harder work and less composed overall than its rear-engined rival? Not unlike the BMW M3/M4, the chassis of the Mercedes could do with more compliance for more control and confidence. When you fly up the hill with a knife between the teeth, vertical body movements are occasionally prone to dent the line, to momentarily push the handling balance off kilter, to call for an ultra-quick action at the wheel. It’s not always a big deal, but it’s a warning of the kind a Corvette or an F-type R might issue. Which comes as a bit of a surprise because in essence the Benz, just like the Porsche, rarely leaves you in doubt about its riveting roadholding and the inherently failsafe handling. But since there is no engine sitting on top of its driven wheels, which are under substantial torque stress when the going gets tough, breakaway is easily induced.

At the dawn of a new era devoted to downsizing, hybridisation, electromobility and fuel cells, V8s will soon be condemned as fossils from a wasteful past – so go and get one while you still can. Because nothing sounds like an eight-cylinder; the blend of generous displacement and eager turbocharging never fails to excite, and a V8 is equally charismatic at a leisurely pace and at full song. This engine is the soul, the essence and the main motivator of the AMG GTS. Funny that a similar hymn of praise can be sung of the flat-six installed in the 911. Now water-cooled but in this particular application still normally-aspirated, the 3800cc motor makes all the right noises, is connected to the throttle pedal via a live wire, and begs to be revved hard to deliver the goods. Purists may prefer the boxer in combination with the seven-speed manual, but in case your left hoof has been numbed into early retirement by too many automatics, the PDK box is a perfectly acceptable substitute to that third pedal. Late next year when the new 992 enters the scene, turbos will be mandatory across the range, so it’s now or never, unless your budget stretches to the GT3.

Porsche 991 GTS, doing its oversteer thing. It'll drift all day...

Before we wrap up, the two muskeeters trumpet down the hill in loose convoy one more time, landing at the bottom of the valley with crackling exhausts, sizzling brakes and liquorice tyres. So what’s the verdict? Which concept works best? Is front-engined superior to rear-engined or vice versa? Which options are essential to further roll out the dynamic envelope? How much GT do you need or allow in a sports car? Decisions, decisions. The Porsche is an emotional masterpiece. It combines the physique of the Carrera S with the heart of the GT3 while consciously avoiding the overly radical aspects of the latter. The 911 has lovely steering which is weighted, damped and calibrated to perfection. It also has impeccable steel brakes, a wizard chassis engineered for an amazing ride/handling balance, a quickshift transmission and an engine that sounds, performs and revs to an infectious degree. In this particular company, however, it could do with a bit more power and torque.

The AMG car earns its merits as compelling autobahn stormer, superfast long-distance cruiser, major scorer in the street-cred sweepstakes and wholly superior SLS replacement. Its intuitive transmission is every bit as clever as the quickest pair of index fingers, the brakes perform with the finality of a guillotine, and the engine develops an incredible physical thrust as it storms through the rev range. It may be 135kg heavier than the Porsche, but the GTS easily wins the infotainment trophy, too, is more lavishly equipped, has a big enough and more practical boot, and oozes presence from all pores. But then it will cost more, too – around £107,000 to the 911’s £91,098 – and it does have weaknesses (compromised packaging, debatable suspension tuning). 

Verdict

Not surprisingly then, the 911 is the purer, more focused and ultimately more dynamic choice. The new Mercedes AMG is neither the perfect GT nor the perfect sports car. But it straddles the two categories with addictive appeal and ability.

By Georg Kacher

European editor, secrets uncoverer, futurist, first man behind any wheel

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