What’s Old Is New Again – The Return Of The Inline-Six
By GREG ACOSTA
JUNE 12, 2019
By and far, the inline-six cylinder has proven itself to be a robust engine configuration over the span of the last 50-plus years. However, in the more modern times, the configuration has fallen out of favor with automakers due to size and space constraints imposed by modern technology and packaging requirements, along with some manufacturing concerns.
With engine parts commonality on the assembly line being placed in ever-higher importance and previous generations of inline-six engines not really being common to any modern engine platform, it is relatively easy to see how they fell out of favor when manufacturers looked to design a new powerplant for a new vehicle.
However, Mercedes-Benz flipped the script, and decided to take all the inherent advantages of an inline-six cylinder engine, and reimagine the engine in a modern, 21st-century way. Addressing all the packaging concerns and engine manufacturing commonality issues and then adding in technologies which have been seen in their Formula One racing efforts, Mercedes has breathed new life into the inline-six cylinder engine and the industry as a whole has taken notice.In his video, Fenske walks us through the Mercedes M256 engine, which entered production a little less than two years ago, and dives into how Mercedes addressed the shortcomings of previous inline-six engines, and made them the new hotness. Wading through his brutally honest opinions of the GLE 450 it resides in, we find a trove of information, as is usually the case in one of his videos.
“Downsizing of engines is becoming a very popular thing [for automakers] to do,” says Fenske. “Where it used to be that you had a popular V8 platform, you could just lop off two cylinders and have a V6 that fits in the same packaging, and can be made in a similar fashion, and makes a lot of sense from a production line.”The challenge of fitting an inline-six cylinder engine into an engine bay that was previously designed for a V6 was no small task. “Mercedes did two clever things here. The first, is they simply reduced the bore size,” explains Fenske. “They went from an 88mm bore down to a 83mm bore.” It makes sense, reducing bore size allows for closer bore centers. Closer bore centers in turn allow for a more compact engine block.
“They were able to take a few inches off the length of the engine simply by reducing the bore and increasing the stroke compared to their V6 engines,” Fenske explains. “The second thing they did was that they electrified the engine. Where you would normally see a torque converter, you now have an integrated starter and alternator. This little pancake motor at the rear, because it acts as a generator, allows them to get rid of the accessory belt and drive at the front of the engine.”
By eliminating the traditional accessory drive on the front of the engine, the overall length of the engine is further reduced, allowing for ample room in the space originally designed for a compact V6 powerplant. Remember when we mentioned that some of the technology from F1 was incorporated as well? That pancake starter alternator motor also happens to produce a whopping 160 lb-ft of torque, which is not only available on demand to boost the engine, but also power the 48-volt electrical system, that is also fueled by regenerative braking.