Inside AMG's new 375kW four-litre V8

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IOL mot jul28 AMG M178 V8 1 . Top view of AMG M178 four-litre biturbo V8 shows the layout of the hot inside V architecture.

Affalterbach, Germany - AMG is, first and foremost, a supplier of high-performance engines - especially V8s, going all the way to the 6.8-litre M100 that took the 300 SEL endurance racer to a magnificent second in the 1971 Spa 24 Hours.

So when head of engine development Christian Enderle says the new M178 four-litre biturbo V8, specially developed for the AMG GT, successor to the iconic SLS, is something special even by AMG standards, it's worth a closer look.

The numbers alone are enough to make you blink: 375kW at 6250 revs and 650 Nm from 1750-4750rpm. Getting them out of an engine that can be run on the street without self-destructing has required some lateral thinking.

The new V8's two turbochargers are mounted side by side in the V of the block, rather than on the outside of the cylinder banks - a layout the AMG whitecoats define as 'hot inside V'. No kidding.

The advantage is that the M178 engine is considerably more compact and much lighter - according to AMG the whole engine weighs only 209kg - and the exhaust gas path is much shorter, which reduces both turbo lag and emissions.

DRY SUMP

IOL mot jul28 AMG M178 V8 2 Cylinder-head cutaway shows direct fuel-injector, four valves per cylinder.

The M178 runs dry-sump lubrication, using a suction pump, a pressure pump and a 12-litre external oil tank. That removes the need for a sump, reducing the overall height of the engine by 55mm and enabling it to be mounted lower in the chassis, lowering the car's centre of gravity for improved handling in corners, while also solving the problem of momentary oil starvation due to oil surge.

The new V8 runs nine litres of oil; the suction pump extracts oil directly from the crankcase, cylinder heads and valve body assembly and delivers it to the external oil tank at up to 250 litres per minute.

The oil stays in the tank for just five seconds before being pumped back into the engine, while on-demand control of the pressure oil pump takes into account the engine revs, load and temperature.

Direct fuel-injection at fuel pressure between 100 and 200 bar from high-speed piezo injectors uses spray-guided combustion to increase thermodynamic efficiency, thereby reducing fuel consumption and exhaust gas emissions.

COOL(ER) RUNNINGS

The engine has a three-phase thermostat and a chain-driven waterpump that pushes 420 litres a minute (that's two full bathtubs) through the water jacket.

IOL mot jul28 AMG M178 V8 3 As always at AMG, each M178 engine is assembled by a single technician, who then affixes a plate with his signature on it to the top cover.

A charge air cooler with its own water circuit and radiator - and very short intake ducting - keep intake air temperature down to a maximum of 180 degrees.

Finally, a two-stage, electronically controlled oil pump circulates the engine oil through the engine and an external engine oil cooler in the front apron of the Mercedes-AMG GT at up to a litre a second.

MAKING ALL THE RIGHT NOISES

An exhaust flap on either side of the rear silencer is actuated depending on the transmission mode, driver's power requirement and the engine speed; at low loads and engine revs the flaps remain closed.

This causes the exhaust gases to cover a longer distance and flow through an additional damping element so that the engine sound is pleasantly subdued and irritating frequencies are effectively suppressed.

When the driver accelerates, the flaps progressively open so that although some of the exhaust gases cover the longer, acoustically dampened distance, most travel the shorter distance - and at full tilt boogie both flaps are wide open, giving the occupants the full benefit of the new engine's sound-track.



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