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Mercedes Brings Back The Inline Six With 408 HP And Marvelous New Technology

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Just a couple of decades ago, silky-smooth inline-sixes purred under the hoods of our cars, and the world was a great place because of it. But those glory days are over, and package-friendly, boring V6s have taken over. Except now, thanks to the car gods, Mercedes is officially bringing its inline-six back, and with a lot of horsepower.


Modern V6s are lame; they sound terrible, they’re not especially smooth, and without turbos or supercharges, they tend to lack low-end torque. That’s why I’m so excited for Mercedes’ recently-announced M256 inline-six engine, an engine that we suspected was on its way into the 2017 S-Class, and perhaps into other Daimler products thereafter.

The engine is part of a new family of engines from the Stuttgart-based automaker—a modular family that includes gas and diesel inline-fours, gas and diesel inline-sixes and a gas V8, all of which have identical bore spacing of 90 mm and identical “interfaces to the vehicle,” which I assume refers to the bell housing bolt pattern. All four of these engines will be offered in the new 2017 Mercedes S-Class.


But the crown jewel of the family is the 408 horsepower gas inline-six.

Mercedes says the inline-six has been “systematically designed for electrification,” and that it will come with an Inline Starter Generator, or ISG, that drives the crankshaft. The ISG is comprised of a motor that starts the engine during engine start/stop events, provides up to 15 kW of boost to move the car off the line quickly, acts as an alternator for the 12-volt system, and provide energy recovery during braking or coasting.

Another benefit of the ISG, Mercedes says, is that, depending on the state of charge of the battery, it can “shift the load point” of the engine. In other words, the motor in the ISG can remove some of the load from the internal combustion engine, allowing the latter to “be operated in a more favorable area of the engine [speed/load] map.”


The ISG is part of a 48 volt system, which drives an electric water pump, an electric AC compressor, and an electric auxiliary compressor that Mercedes calls an eZV. This means there’s no belt-driven accessory drive, reducing overall engine length—a godsend for an inherently long engine like an inline-six.

The electric compressor is basically a 48-volt turbo that crams air into the cylinders when the engine is at low RPMS and the big exhaust-driven turbo isn’t cutting it. Mercedes says the eZV accelerates to 70,000 RPM within 0.3 seconds, and that, between it and the ISG, this inline-six should get off the line quickly with “no turbo lag.”


So to recap: this 3.0-liter turbocharged inline-six, with its electric motor/generator, electric turbocharger, electric water pump and electric AC compressor, is a thoroughly advanced contraption that promises more than 408 horsepower and 370 lb-ft of torque.

The car gods have answered our prayers.