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The grandaddy of Mercedes inline-sixes: the direct-injected (in 1954!) M198 that powered the 300SL.

What’s old (and revered) is new again

Apart from top brass and various other engineering true believers at Mercedes-Benz, perhaps no one was more delighted than me when it was confirmed a couple of years ago that Mercedes was introducing a new architecture for inline 6-cylinder engines, an engine layout that long served as a cornerstone for the brand’s reputation for consummate powertrain performance and refinement.

The inline six became synonymous with Mercedes in its “modern” era that started roughly in the 1950s and appeared in some form or other for the next half-century (including the seminal 3.0-L Bosch direct-injected M198 for the legendary 300 SL), with the company cutting ties with its last I-6 in 1998.

In October, Mercedes made known the basic details of the new inline 6-cylinder family, the foundation of which is a modular 500-cc cylinder—not to mention the incorporation of new-age electrification features; Automotive Engineering European correspondent Stuart Birch delivers the initial rundown at: .

I’ve certainly missed the I-6. As many know, inline sixes gradually became a vehicle-development liability as front-drive vehicle architectures began to dominate and, more directly, as global frontal-crash regulations tightened. Inline sixes typically were too long to be effectively packaged in transverse-engine platforms (although it was done)—and the straight six’s physical length similarly made it difficult to fit one even in a platform designed for longitudinal placement, because the unyielding engine didn’t permit enough energy-absorbing crumple zone in frontal impacts.

Only BMW—which over the years became more famous for the straight six than even Mercedes—somehow kept the faith. When inline sixes started to bite the dust all over the globe, I repeatedly asked senior engineers, designers and executives how BMW could somehow get on the right side of crash physics when everyone else claimed it couldn’t be done. The usual answer, I’ll paraphrase, tended to: “Perhaps it’s because we make the inline six-cylinder a priority.”

It surely must have been difficult for those concerned with engine superiority to turn their backs on the I-6 layout’s inherent balance and outstanding torque characteristics. Then there are the considerable design and manufacturing advantages compared with a V-6, as Ron Kociba, former General Motors chief engineer of the "zig-when-everyone-else-is-zagging" Vortec 4200 I-6 never tired of explaining. It’s ironic those benefits are being revisited as cost advantages when compared with a V-6, given that one justification Mercedes and others cited for moving to vee-arranged 6-cylinder engines was modular compatibility with V-8s. My, how the world has changed: now the critical cost-sharing modularity metric is with inline 4-cylinder engines, not V-8s.

The German luxury-car makers didn’t have an exclusive on the I-6 secret—Toyota, for one, authored some magnificent inline sixes, including my personal craving, the ballistic twin-turbocharged 2JZ-GTE 3.0-L used in the last-generation Supra—but for Mercedes and BMW, there’s no doubt the format is indelibly tied to those brands.

What makes it all the better for straight-six disciples: as with the M198 from the 1950s, Mercedes is launching its new-generation I-6s with the era’s most bleeding-edge technology: integration with a 48-volt electrical system that facilitates several nifty efficiency and performance game-changes, included an electrically-accelerated turbocharger as the last word in eradication of turbo “lag.”

What’s old really is new again. In Mercedes’ revival of the inline-six, “old” may equate to vintage attributes, but these new engines promise to be anything but vintage. What a world.

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