Cutaway of M256 straight six turbopetrol shows the deep cylinder head, turbo mounted right up against the cylinder head and side-mounted ancillaries.

Stuttgart, Germany - Mercedes-Benz is calling this the biggest engine initiative in its history; within little more than a year after the introduction of its all-new OM654 two-litre turbodiesel four in the second quarter of 2016, it will be followed by four more additions to this new family of engines, all based on a modular architecture with identical 90mm cylinder spacing and an individual cylinder capacity of just less than 500cc.

Thus the range will include a two-litre turbopetrol four, three-litre turbo sixes in both petrol and diesel, and a four-litre twin-turbo V8 - all with identical mounting points, bell-housing faces, wiring connections, and connections for fuel, coolant and oil cooler hoses, which will make producing variants of the same model with different engines on a single assembly much simpler and more cost-effective.

And here's the first surprise: Mercedes has gone back to the traditional straight six layout, rather than the more compact V6 format it has favoured in recent years, presumably for its perfect primary and secondary balance, which gives it incomparably smooth running. (It also raises the possibility of a magnificent six-litre V12 later on that would require very little extra development, but that's pure speculation on our part.)

The three-litre M256 turbopetrol six - which will be launched in 2017 in the new S-Class - introduces a 48 volt electrical system that includes an integrated starter-alternator and an electric auxiliary compressor to provide instant boost, thus preventing turbo lag. The integrated starter alternator not only provides smooth, virtually seamless starting but also functions as a mild hybrid, providing a little extra power up to 2500rpm, and recoups as much as 12.5kW of energy lost under braking and on the overrun, using it to charge the battery.

The 48 volt system also powers an electric water-pump as well as the air-conditioning compressor, so there's no need for a belt drove on the front of the engine, reducing the length penalty inherent in moving from a V6 to an inline six layout.

The deep cylinder head, visible in the cutaway drawing above, physically separates the inlet and exhaust plumbing, allowing the turbocharger to be mounted very close to the exhaust valves and, for the first time on a Mercedes-Benz, switchable variable cam timing.

Stuttgart claims that the M256 is good for about the engine same power and torque as the current V8, with more than 300kW and 500Nm, while emitting about 15 percent less CO2 than the current V6.

OM656 three-litre straight six turbodiesel

This, says Mercedes-Benz, is the most powerful passenger-car diesel engine in its history. It has an aluminium block with Nanoslide bore coatings and high-strength steel piston with stepped-bowl combustion chambers, two-stage turbocharging, and variable valve timing.

The maker quotes a power output of more than 230kW, compared to 190kW for the current OM642 three-litre turbodiesel, while using more than seven percent less fuel.

As with the already-launched OM654 two-litre turbodiesel four, it's been designed with an eye to compliance with future 'real world' emissions regulations, with dynamic multi-path exhaust gas recirculation and the twin-scroll turbo mounted as close as possible to the exhaust valves to minimise heat loss.

M176 four-litre biturbo petrol V8

The 3982cc V8 will also be launched in the new S-Class next year, rated at more than 350kW and about 7800Nm, on tap from around 2000rpm - about 4.5 percent better than the 335kW of its predecessor - while using more than 10 percent less fuel.

It uses variable cam timing to shut off four cylinders under part load, reducing pumping loads and improving the efficiency of the remaining four cylinders by raising the revs to the range where they function best.

M264 two-litre turbo petrol four

This sporty four-cylinder powerhouse is rated for about 100kW, thanks to a twin-scroll turbocharger, variable cam timing, a belt-driven 48 volt starter-alternator and a 48 volt electric water pump.

Previously, if you wanted three-digit power output from a Mercedes engine, you had to go to a bigger six-cylinder unit; now you can get it in a two-litre turbofour with considerably lower fuel-consumption.

The current S500 was the first petrol-engined Mercedes with a particulate filter to remove microscopic soot granules from the exhaust gases; during 2017 more new S-Class sedans with the M256 straight six and M264 turbofour will be introduced, also with particulate filters as standard.

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