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Next-gen Mercedes engines bring 48V electrics and the return of the straight six

New modular engine family will now include new four-cylinder, inline-six, and V8 engines, with 48V architecture, electric turbocharging, and variable valve timing. Engines to debut in next year’s S-Class facelift.

Following the debut of their new engine family with the 143kW/400Nm 2.0-litre four-cylinder turbocharged diesel OM654 engine in the new E-Class earlier this year, Mercedes-Benz has announced the rest of the line-up of the engine family, which comprises of four new engines. 

Headlining the new engine range are two new inline-six mills, a 3.0-litre turbocharged petrol unit with outputs in excess of 300kW and 500Nm called the M256, and a 2.9-litre turbocharged diesel unit which produces ‘more than 230kW and over 650Nm of torque’ christened the OM656. These new engines are the first inline-six engines seen from the brand since 1999, when Mercedes-Benz discontinued the M104 in favour for a more compact V6-configuration.

Built with a 500cc per cylinder displacement, the new M256 3.0-litre inline-six petrol unit is said to be Mercedes-Benz’s first such powertrain that has been systematically developed for electrification from the start. 

The new inline-six mill has a 55kW/20Nm higher output, while producing 15 per cent less CO2 emissions. 

Armed with a 48V electrical system, the engine does away with belt-driven ancillaries such as the water pump and air conditioning compressors in favour of being powered by an ‘Integrated Starter-Alternator’ (ISG) system. This arrangement is said to reduce both engine size as well as its complexity. As for powering onboard lighting, instrumentation, and control units, the powertrain still comes with an existing 12V system.

The ISG not only serves as an alternator, but it also acts as a mild-hybrid motor to give the engine an immediate 15kW/220Nm boost upon start-up, facilitates energy recovery, and allows for an ‘almost imperceptible’ restart of the engine with the auto start/stop feature.

The use of a 48V system also allows engineers to fit on an electric auxiliary turbocharger (eZV)  that could spin up to 70,000rpm within 0.3 seconds to deliver an immediate throttle response and zero lag. 

Compared to the outgoing 3.0-litre V6 petrol unit, the new inline-six mill has a 55kW/20Nm higher output, while producing 15 per cent less CO2 emissions. 

As for the OM656 2.9-litre inline-six diesel engine, it features an all-aluminium engine block with steel pistons, which it uses to its advantage in delivering better power delivery and fuel efficiency. Thanks to the differences in thermal expansion and conductivity of the steel used in the pistons and the aluminium engine block, engineers were able to reduce internal friction by up to half, whilst improving its thermodynamic efficiency.

Coming out in a post-Dieselgate climate, Mercedes-Benz says that the new OM656 engine has been designed to meet future Real Driving Emissions legislation. As such engineers have tweaked several aspects of the engine, with its pistons adopting a new ‘Stepped-bowl’ combustion process that is said to deliver a more efficient and higher fuel burn rate than before and especially reduced particulate emissions. 

Its Camtronic switchable exhaust camshaft and near-engine configuration results in better exhaust aftertreatment, while new insulation and improved catalyst coatings reduces the need for the engines to warm-up during cold starts.

All things considered, Mercedes-Benz says the new inline-six diesel engine consumes seven per cent less fuel while delivering over 40kW and 30Nm more than its 3.0-litre V6 turbocharged diesel predecessor could manage. 

Complementing the existing OM654 four-cylinder diesel engine is a new 2.0-litre four-cylinder turbocharged petrol mill. While Mercedes-Benz aren’t releasing exact figures, the new engine is said to achieve a specific output of 100kW per litre, or a power output of 200kW. 

Codenamed the M264, the new engine utilises a twin-scroll turbocharger, intake Camtronic variable valve technology, and a 48V electrical system. Unlike the 48V system used in the M256 inline-six engine, the M 264’s 48V system is used to power a belt-driven starter-alternator motor (BSA) and electric water pump. 

Like the mild-hybrid capabilities of the inline-six petrol’s ISG system, the BSA is a milder version that is meant to improve fuel efficiency where possible. According to Mercedes-Benz, the BSA is able to boost the engine-speed range by up to 2,500rpm, facilitate an energy recovery of up to 12.5kW, coasting with the engine off, allow extended start/stop with intelligent engine shut-off at low speeds, and deliver ‘virtually imperceptible’ starting and accelerating of the engine from start-up.

Standing as the cream of Mercedes-Benz’s new engine line-up is a new M176 4-litre biturbo petrol V8, which was developed by AMG. According to Mercedes-Benz the new V8 power unit cranks out 350kW and ‘approximately’ 700Nm of torque, a significant hike over its 4.7-litre M278 (as used in the current S500) predecessor’s 335kW and 700Nm of torque.

Interesting enough the new M176 engine boasts a similar displacement and power output AMG’s current M 177 4-litre biturbo V8 in the C63, along with the same ‘hot inside V’ turbocharger arrangement that relocates the turbochargers to the top of the engine - between its cylinder banks. That being said the new M 176 engine produces around 50Nm more torque than the AMG version used in the C63. 

Despite the extra power on hand, the new engine manages a 10 per cent lower fuel consumption figures over its predecessor.

This is achieved through several key optimisation done to the engine, chief among which is the cylinder deactivation, which is active at engine speeds of between 900 to 3,250rpm and the driver has left the Dynamic Select switch in ‘C’ or ‘E’. While no fuel consumption or CO2 emission figures are stated, Mercedes-Benz claims that the M176 is one of the world’s most economical V8s. 

For now Mercedes-Benz has confirmed that the new 3-litre turbocharged inline-six petrol and 4-litre biturbo V8 petrol units will make its debut on the facelifted S-Class, which is slated to be introduced next year. Although Mercedes doesn’t mention where either the 2.9-litre turbocharged inline-six diesel or 2-litre four-cylinder turbocharged petrol will appear, we can be certain that it will find its way into their model line-up soon enough. 

Are you excited about the return of the straight six? Tell us what you think in the comments below.