New V8 biturbo petrol engine (M 176): Number of cylinders to suit the requirements

Dynamic power delivery combined with high efficiency: the new biturbo is one of the most economical V8 petrol engines in the world. The special features of the V8 (internal code: M 176) include cylinder shutoff at part load. The M 176 will launch with this technology next year in the new S-Class.

Developed by AMG for Mercedes-Benz, the hallmarks of the new V8 biturbo are exemplary efficiency and environmental compatibility as well as superlative performance. From its 3982 cc displacement, the new V8 biturbo produces over 350 kW (476 hp) with a maximum torque of around 700 Nm from 2000 rpm. The new engine will consume over 10 percent less fuel than its predecessor, which is rated at 335 kW (455 hp).

For even lower fuel consumption, when operated at part load the new M 176 shuts off four cylinders simultaneously by means of CAMTRONIC valve timing. This reduces the pumping losses while improving the overall efficiency of the remaining four cylinders by shifting the operating point towards higher loads.

The cylinders are turned on and off by the interplay between engine control and actuators on the cylinder head. The switchover to four-cylinder operation is accomplished by eight actuators that act on the axially movable cam parts of the intake and exhaust camshafts via a selector. These cam parts are held on the carrier shaft by gears and are locked in the respective end positions by means of a locking mechanism. The intake and exhaust valves of cylinders 2, 3, 5 and 8 do not open due to the zero-lift cams of the cam parts. At the same time, the fuel supply and ignition are deactivated, so that no unburned mixture is left in the deactivated combustion chamber.

Cylinder shutoff is active in the engine-speed range between 900 and 3250 rpm, provided the driver has selected mode C or E with the DYNAMIC SELECT switch. Cylinder shutoff is inactive in all other transmission modes. As soon as the driver requests higher engine power via the position of the accelerator or as soon as the engine speed goes above 3250 rpm, cylinders 2, 3, 5 and 8 are reinstated within a matter of milliseconds. The transition between the two operating modes is seamless and with no loss of comfort for the occupants. The main menu in the instrument cluster shows whether the engine is currently in four- or eight-cylinder mode.

The new V8 biturbo employs a centrifugal pendulum to reduce both the fourth-order vibrations in eight-cylinder mode as well as the second-order vibrations in four-cylinder mode.

A combination of biturbocharging and direct petrol injection with spray-guided combustion increases the thermodynamic efficiency, thereby reducing the fuel consumption and exhaust emissions. Particularly fast and precise piezo injectors spray the fuel at high pressure into the eight combustion chambers. Multiple injection occurs on-demand, ensuring a homogeneous fuel/air mixture. The delivery of fuel is electronically controlled and fully variable for a fuel pressure between 100 and 200 bar.

The engine is of closed-deck construction, which means that the engine block cover plate is extensively closed in the area around the cylinders. The engine block is of an aluminium alloy and produced by permanent mould casting. This ensures extreme strength while keeping the weight as low as possible, and allows high injection pressures of up to 140 bar. The further-improved NANOSLIDE® coating of the cylinder liners reduces the friction loss while contributing to excellent efficiency. The cylinder head uses an aluminium-zirconium alloy, which is a better conductor of heat than the standard aluminium alloy.

"Spectacle honing" is another measure for reducing the friction and therefore consumption: in this complex process, the cylinder liners receive their mechanical surface treatment when already bolted in place. A jig resembling spectacles is bolted to the engine block in place of the cylinder head, which is mounted later. The honing of the engine block already produces the same state of stress as when the cylinder heads are mounted. For this reason, the tension of the piston rings can be reduced, which leads to a further reduction in friction loss and lower oil consumption.

For an exceptional engine response and low exhaust emissions, the two turbochargers are positioned not on the outside of the cylinder banks, but between them in the "V" – experts call this the "hot inside V". In the interests of thermal protection for the engine components, the manifolds and exhaust turbochargers are specially insulated.

The efficiency-raising measures include the low-friction drive of alternator and refrigerant compressor by means of two short four-groove belts. The water pump is chain-driven by the timing assembly. A two-stage feedback-controlled oil pump circulates the engine oil. It varies the flow rate depending on the required load and engine speed, thereby helping to save fuel.

The M 176 has exhaust aftertreatment with two catalysts directly mounted on the engine and on the underfloor. The as-standard particulate filter is part of the exhaust system under the floor.

The M 176 is produced at the Untertürkheim plant in Stuttgart.

The data of the new engine in comparison with its predecessor:

Engine

 

M 176

M 278

No. of cylinders/arrangement

 

8/V

8/V

Displacement per cylinder

cc

498

583

Displacement

cc

3982

4663

Cylinder spacing

mm

90

106

Bore

mm

83

92.9

Stroke

mm

92

86

Bore/stroke

 

1.1

0.92

Rated output

kW/hp

over 350/476

335/455

Peak torque

Nm

approx. 700

700

Compression ratio

1:

10.5

10.5

Emissions standard

 

EU 6

EU 6

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