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Mercedes-Benz has revealed full information about its new 4.0-litre twin-turbocharged V8 engine that will power the forthcoming 2015 Mercedes-AMG GT and next-generation C63 AMG.

Codenamed the AMG M178, the 3982cc bi-turbo eight-cylinder will produce peak outputs of 375kW (at 6250rpm) and 650Nm (between 1750 and 4750rpm) in its application in the GT — similar to the Porsche 911 Turbo’s 383kW/660Nm six-cylinder.

These outputs were revealed in a teaser video last month, but all the tech specs are now available.

Each engine will, according to AMG policy, be assembled in Affalterbach by one person from go to whoa, and sport a signed plate attesting the fact. 

Mercedes-AMG 4.0-Liter Biturbo-Motor (M 178); 2014

The 4.0-litre twin-turbo V8 is closely related to the manic 265kW 2.0-litre turbo four in the A45, CLA45 and GLA45 AMG models, sharing the same bore/stroke ratio of 83 x 92mm. Maximum engine speed is 7200rpm. 

The shift to a downsized twin-turbo V8 reflects environmental regulations: this new engine meets Euro 6 requirements out to 2016. AMG says it will consume less than 10L/100km on the NEDC combined cycle. 

It is nevertheless more potent than the AMG 6.2-litre atmo V8 used in models such as the outgoing 336kW/610Nm C63 AMG (373kW/610Nm in Edition 507 form), though this engine has been stretched to 386kW/630Nm before. 

Whether the full-fat 375kW/650Nm version of this engine will carry over to the new C63, due to premiere at the Paris motor show this October, or whether it will get a slight de-tune, remains unknown.

Mercedes-AMG 4.0-Liter Biturbo-Motor (M 178); 2014

Recent reports out of Europe indicate the Mercedes-AMG GT, meanwhile, will premiere online on September 9 before appearing in Paris alongside the C63. 

Referring to this new engine, Tobias Moers, chairman of the Board of Management of Mercedes-AMG GmbH, called V8 engines “an integral part of the AMG philosophy and the brand’s commitment to ‘Driving Performance”.

In other words, emissions requirements demand smaller displacements with more forced induction, but the big V8 appears to be as central to AMG as ever. The AMG V8 story dates back to 1967 with the M100 in the 300 SEL 6.8 AMG racing car.

Highlights of the new engine include third-generation piezo injectors handling the direct fuel injection, an aluminium crankcase that is strong enough to handle injection pressures of 130 bar while cutting weight and cylinder bore surfaces with Nanoslide technology that makes them twice as hard as cast-iron. 

Mercedes-AMG 4.0-Liter Biturbo-Motor (M 178); 2014

Though around sine 2000, this latest iteration of Nanoslide is being deployed in the 2014 season Mercedes F1 V6 turbo engine that is currently spanking its rivals.

The engine also has forged aluminium pistons and low-friction piston rings, while the use of a dry sump (with a suction pump and external oil tank) means the conventional oil pan can be removed, allowing the engine to be dropped 55mm and improving a car’s centre of gravity. 

The cylinder heads in the AMG 4.0-litre V8 biturbo engine are made of a zirconium alloy for “maximum temperature resistance and thermal conductivity”. The engine itself is relatively compact, in no small part due to the placement of each exhaust gas turbos inside the V, rather than on the outside of the cylinder banks.

Fun facts: the maximum charge pressure is 1.2 bar and the turbochargers have a maximum speed of 186,000 revolutions per minute. During combustion, 2.3 times more oxygen atoms are pressed into the turbocharged engine as would be the case in a naturally aspirated engine.

Mercedes-AMG 4.0-Liter Biturbo-Motor (M 178); 2014

But as we know with an AMG engine, it’s the sound that really counts. Despite losing 2200cc of displacement and having turbos strapped on, the company insists this new engine still sounds the part.

The new GT has a sports exhaust system with fully variable exhaust flaps on either side of the rear silencer that makes it organically louder or quieter depending on which driving mode is engaged. Under full load at higher engine speeds, both flaps are fully opened.

“Excitement, emotive appeal and recognition value: at Mercedes-AMG engine sound is an important target during development,” the company says. 

Testing on this engine was rigorous, according to AMG, and included “all climatic zones and route profiles from the icy cold of northern Sweden to the merciless heat of Death Valley (USA), from fast laps on the North Loop of the Nürburgring and high-speed circuits in Nardo (Italy) and Papenburg to stop-and-go city traffic during rush hour”. 




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