Mercedes-AMG’s SLS departure opens door to new GT

  • 16-Sep-2014 04:07 EDT
Merc09-14 AMG-GT hi res 2.jpg

Mercedes-AMG's new GT has an equally new V8 4.0-L biturbo engine.

How can Mercedes-AMG top its gull-winged SLS that has just eased out of production? It doesn’t try. Instead, the SLS "replacement" is less costly, less radical, more practical, but still bristling with the sort of technology it will need to find success in the rarefied reaches of the ultra-premium super-high-performance sports car market.

The immediate impression of the aluminum intensive Mercedes-AMG GT is from its classic coupe design: front/mid-engine beneath a long hood, rear-wheel drive, double wishbone suspension front and rear, huge wheels, two-seat high-tech cockpit, cab-rearward fastback styling, subtle mix of aggression, with at least a hint of modesty—and regular doors.

Powering the car is an all-new biturbo 4.0-L V8 available with two power levels: hot (GT) at 340 kW (456 hp) and exceedingly hot (GT S) at 375 kW (503 hp). To ensure the power-to-weight ratio—a best of 3.08 kg/hp (6.79 lb/hp)—puts the new car firmly in the ultra-quick realm, aluminum is the favored material of construction together with magnesium for the front module, although steel is used for the tailgate. The result is a best 0-100 km/h (0-62 mph) time of 3.8 s and a top speed of 311 km/h (193 mph).

Daimler Group Research and Mercedes’ Development boss, Prof. Dr. Thomas Weber, stresses the car’s technology link between road and track: “How do you combine supreme performance with maximum efficiency? That takes true engineering skill, and motorsport is the best imaginable training ground. The fact is, F1 [Formula One] and production cars were never as close as they are today.”

Weber underlines the importance of AMG being “seamlessly integrated” into Mercedes’ global R&D network, which encompasses 14,000 specialists: “AMG has unlimited access to this phenomenal expertise. It is all about performance at Mercedes-AMG.”

Mercedes-AMG Chairman, Tobias Moers, said of the car: “The new GT is the second sports car developed entirely in-house. The result is a thoroughbred sports car—but not a successor to the SLS. For it, we opted for the proven vehicle architecture of the SLS: the transaxle principle with front/mid-engine and dual-clutch transmission at the rear axle, the whole connected via a torque tube. In our opinion this is the best solution if you want to make a sports car really fast”

He emphasized the importance of the powertrain: “Our new V8 engine family has a big career ahead of it, and not just in the GT. It provides the basis for future AMG engines and the next generation from Mercedes-Benz.” He added: “We are already working with our F1 colleagues in Brixworth, UK, on the next-generation of AMG four-cylinder engines.”

With any high-performance coupe, convincing aesthetics are an absolute imperative. Gorden Wagener, Daimler Vice President of Design, has overseen a visual signature quite different to that of the SLS.

He describes the GT as having “positively arched surfaces” including a dome-shaped arched roofline. Doors are frameless. It has no distinct shoulder lines, but two modest lower lines to accentuate length. Side air outlets, features on high-performance Mercedes since the 1950s, are not too overt. LED headlamps are prominent and incorporate three high-beam reflectors. In keeping with a Mercedes trend, the GT gets large front air intakes and an AMG signature A-wing with front splitter on the lower section of the front apron.

Aerodynamics (Mercedes-AMG has not released Cd or downforce figures) include use of a deploying rear aerofoil, a rear diffuser is flanked by large twin exhaust tailpipes, and the car has an “extensively clad” underfloor.

Of the use of magnesium for the front module, the extremely light element at the front is said to reduce the inertia ahead of the front axle, improving the vehicle’s agility. More than 90% of the weight-optimized spaceframe is made from aluminum components.

Bodyshell weight is 231 kg (509 lb) and torsional stiffness is said to be very high, but Mercedes has elected to give no specific figures. The heaviest curb weight quoted is for the GT S at 1645 kg (3627 lb) with a fuel tank 90% full, 68-kg (150-lb) driver, and 7 kg (15 lb) of luggage aboard. The lightest, for the GT, with 90% fuel but no driver or luggage, is 1540 kg (3395 lb). The best “standardized” fuel consumption is 9.3 L/100 km.

The engine, designated M178, is a biturbo 4.0-L, so could be described, in relative terms, as “downsized.” A V8 configuration in a car of this caliber is a must, said Moers: “V8 engines are an integral part of the AMG philosophy.”

The turbos are positioned inside the 90-degree V of the 209-kg (461-lb) dry weight engine to provide compact packaging but also fewer exhaust emissions and better low-end response, so reducing any lag. With 650 N·m (479 lb·ft) on tap from 1750 to 4750 rpm for the GT S, that is not likely to be a problem.

Dry-sump lubrication is used, facilitating a reduced height engine position—down 55 mm (2.2 in)—to aid a low c.g. (center of gravity). Lubrication uses a suction pump, pressure pump, and an external 12-L (13-qt) oil tank. The system circulates 9 L (10 qt) of engine oil. The suction pump extracts oil directly from the crankcases, zirconium alloy cylinder heads, and valve body assembly to deliver it to the external oil tank via an output of up to 250 L/min (66 gal/min). Lubricant stays there for 5 s and is then pumped back around the engine. Mercedes claims an engine “world first” for the combination of biturbo-in-a-V and dry-sump solution.

The engine is a close relation—albeit twice the size—of the 2.0-L unit used in AMG versions of the A-Class compact, which is claimed as the most powerful series production four-cylinder in the world.

The M178, with third-generation direct injection and piezo injectors, conforms to Euro 6 emissions standards. Injection pressures are up to 130 bar (1.9 ksi).

The crankcase is closed deck. Cylinder bore surfaces use Nanoslide technology, which Mercedes describes as making them twice as hard as regular cast-iron linings. It is also used for the F1 V6 turbo engine.

To help further reduce friction losses, “spectacle honing” is used. Mercedes describes the process as including cylinder liners being given their mechanical surface treatment when bolted in place: A jig resembling spectacles is bolted to the crankcase in place of the cylinder head mounted later. Any cylinder warping that might occur during final assembly is therefore taken into account or eliminated as the cylinder liners are honed. The engine uses forged aluminum pistons and a low-friction piston-ring design.

A charge-air intercooler has a separate low temperature water circuit. An exhaust system with fully variable exhaust flaps is fitted, to provide a “motorsport-like sound” or something more muted when appropriate.

For the hand assembly of each M178 engine, AMG applies its “one man, one engine” process. The engine fitter’s signature appears on a plate fixed to the unit.

The engine drives through a seven-speed dual-clutch transmission in transaxle configuration, a la SLS, with several driver-selected modes from “controlled efficiency” to “race” (on the GT S). There is also a driver-preference “individual” setting.

As for elastokinematics and engine mountings, says Moers: “We have engine movement in the car fully under control!” That control involves the use of dynamic mounts, with those of engine and transmission each actuated independently of the other. The combination of selectively variable mounts and a transaxle drivetrain is regarded as “unique” by Mercedes-AMG.

Double-wishbone suspension is used front and rear, which is adopted straight from motorsport, according to Mercedes. Extensive use is made of aluminum. AMG Ride Control sports suspension with electronically controlled damping is standard on the GT S.

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