Fifteen years ago, Mercedes-Benz abandoned its inline-sixes in favor of V-6s. “Half of our engine guys were sad when we switched from the inline-six to the V-6 layout,” one of Daimler’s engineers remembers. “Now it’s the other way around.” Mercedes is pulling an about-face, returning to the straight-six configuration for the same reasons that originally had it embrace the V-6.
Back then, a common parts and production strategy dictated the switch. Daimler had developed a generation of V-6 and V-8 engines with common parts. (The last remnant of that era is the loosely related 6.0-liter V-12 that sits under the hood of the 600 and AMG 65 models.)
The desire for commonality now means combining four- and six-cylinder engines. V-8s have become something of a niche product, and that’s why their development?and that of V-12 engines?is being delegated to AMG. That’s true even for V-8 engines that are used in non-AMG cars. Henceforth, the inline-four and inline-six engines will be manufactured on the same lines. BMW, by the way, does a similar thing, and the Bavarians have expanded their approach to three-cylinder engines, in which Mercedes has no interest.
The engine that interests us most is the 3.0-liter straight-six known as M256 (pictured above). It’s presented in a high-output version that, according to Daimler engineers, makes “more than” 402 horsepower (the output, coincidentally, that was delivered by the nat...