Mercedes-Benz S-Class to get new V8 and inline 6cyl engines

Six-cylinder inline petrol with 48V system 

The S-Class will also receive a new six-cylinder inline petrol engine (codenamed M256) during 2017.

It’s the first engine that Mercedes has designed for electrification from the outset, and is intended as a flagship for a philosophy of mild hybridisation that will underpin the new engine family and ensure the German company can meet stringent economy and emissions rules. 

The new engine has an a 48V electrical system which serves not only the car’s high power consumers, such as the water pump and air-conditioning compressor, but also an Integrated Starter-Alternator (ISG) and electric auxiliary compressor (eZV), which combine to produce a power boost that negates turbo lag.

The claim from Mercedes is that the engine offers the performance of an eight-cylinder engine but emissions and economy that are closer to a four-cylinder unit, in addition to providing refinement of a six-cylinder.

Power output and torque are approximately 402bhp and 369lb ft respectively compared with the 328bhp and 354lb ft of the outgoing M276 V6. CO2 emissions have been reduced by around 15% and, like the new V8, a petrol particulate filter will be fitted to trap soot particles. The filter will be gradually introduced in other new and facelifted vehicle models and new engine generations.

Although inline six-cylinder engines are seen as unfashionable, Mercedes believes the layout offers packaging advantages when combined with the 48V electric system and ISG. The absence of a belt drive makes the engine shorter, and there’s space for ancillary components to be sited on either side of the inline cylinder configuration.

Six-cylinder inline diesel with 308bhp 

Another new engine is a six-cylinder inline diesel (codenamed OM656), which is the most powerful passenger car diesel engine ever to be built by the company and will sit at the top of its diesel line-up. Power has increased to 308bhp from the 254bhp of the outgoing V6 diesel but the engine uses 7% less fuel.

This unit incorporates a host of technology to boost efficiency and power delivery, such as a stepped-bowl combustion process, two-stage exhaust turbocharging and, for the first time, the use of ‘Camtronic’ variable valve timing. 

Its design features a combination of aluminium engine block and steel pistons as well the use of Nanoslide - an extremely thin, low-friction coating of the cylinder walls, two measures that reduce friction. The engine also uses multi-way exhaust gas recirculation and a near-engine exhaust aftertreatment.

Four-cylinder petrol with 134bhp per litre

The fourth engine in the roll-out is a two-litre inline four-cylinder petrol (M264), which Mercedes claims has a specific output of around 134bhp.

The engine’s special features include twin-scroll turbochargers which merge the exhaust gas ducts of cylinder pairs in the flow-optimised manifold. This turbocharging concept with systematic cylinder flow separation produces high torque in the low-rpm range together with high specific output. 

The engine also has a belt-driven 48V starter-alternator (BSA) that is responsible for for fuel-saving hybrid functions such as energy recovery and provides an engine speed boost at low revs. 

Merc's engine tech at a glance

48V electrical system

Supplies four times the power of a 12V system at the same current, and can power both new devices such as the electric auxiliary compressor (eZV) and existing ones like the aircon compressor.

Petrol particulate filter

More commonly found on diesels, Mercedes has used a particulate filter on the S500 for two years and will fit it to the M256 and M176 petrol engines. The PPF is made of a material called cordierite, known for heat resistance properties.