What’s Old Is New Again – The Return Of The Inline-Six

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Thread: What’s Old Is New Again – The Return Of The Inline-Six

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    What’s Old Is New Again – The Return Of The Inline-Six

    What’s Old Is New Again – The Return Of The Inline-Six
    Enginelabs
    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.

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    Re: What’s Old Is New Again – The Return Of The Inline-Six

    This guy throws statements in there that are completely untrue such as saying you can put the catalytic converter closer to the exhaust ports in an in-line six cylinder than you can in a V6 configuration. Horse hockey. That makes no sense whatsoever. He also did a video on the placement of the turbocharger within the V of a V6/V8 and stated that the turbo could be mounted closer to the exhaust ports than the traditional layout thereby reducing lag. Again, horse hockey. He makes statements that are totally wrong. Is the in-line six smoother? Yes. But, don't believe everything this guy says.
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    Re: What’s Old Is New Again – The Return Of The Inline-Six

    The bigger trend seems to be turbo 4s in everything, it amazes me that Benz and others have been able to get away with it. I'll take an I6 in a luxury vehicle any day of the week.
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    Re: What’s Old Is New Again – The Return Of The Inline-Six

    The Ford ten speed hybrid offered as an option in the Explorer and Aviator uses a thin electric motor between the ICE output and the input to the torque converter. The third picture in the link below has a cutaway view. The concept is to use this motor/generator as either a torque adder or power source - fuel savings being less of a concern.

    https://www.sae.org/news/2019/05/202...rid-technology


    For the MHT, it has 90% parts commonality with the conventional 10R automatic transmission and is only marginally longer overall, meaning it can go down the same manufacturing line as the conventional transmission, while the MHT’s extra overall length can be easily accounted for by altering driveshaft length.

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    Re: What’s Old Is New Again – The Return Of The Inline-Six

    For an engineer, he should know the reason that this system does not respond as smoothly to his throttle input - a motor that can either draw or add torque located between the ICE and the transmission means that the control module must torque balance the shifting elements in the 10 speed case AND the motor, when acceleration is demanded. That is a lot of complex code writing. I read a short review on the hybrid Explorer that mildly complained about lack of smoothness. As time goes on, I suspect this type of system will get smoother.

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    Re: What’s Old Is New Again – The Return Of The Inline-Six

    I remember liking the I-6 in the Trailblazer back in the day.

    Always heard at the time it was the future of 6 cylinder engines and then they faded again.

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    Re: What’s Old Is New Again – The Return Of The Inline-Six

    Looking forward to the engineering solutions OEMs employ putting a transverse I6 in FWD models.

    When the V8 was available in nearly everything, the V6 made economic engineering sense. Now that the I4 is the go-to, the I6 has economies.
    The bottom line is- the industry outside of trucks will soon be a majority of 4s, with a smattering of 6s, 8s and EVs. Whether they're inline or V is of little consequence.

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    Re: What’s Old Is New Again – The Return Of The Inline-Six

    One reason the American industry moved away from straight 6s and 8s in the 30s and 40s was that the long crankshaft became easier to bend as engines became more powerful. Before WWI, luxury makes used huge, low rpm 6s, except Cadillac, which went directly from 4s to V8s in 1915.

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    Re: What’s Old Is New Again – The Return Of The Inline-Six

    first thing cutting down a V8 for a V6 does NOT work well as 90 degree V6's are rough running VS a 60 degree one and packaging wise a V configuration almost requires a short stroke engine as longer stroke and higher decks cause the engine to GROW in height AND width

    normally a LONG stroke small bore engine is MORE efficient than a short stroke BIG bore engine

    thirdly most cars / SUVS ETC are going to be boosted 4 CYL engines and a six made from a four is a cost saving endeavor for the LOW volume the sixes will likely have going forward

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    Re: What’s Old Is New Again – The Return Of The Inline-Six

    Quote Originally Posted by ral1960 View Post
    One reason the American industry moved away from straight 6s and 8s in the 30s and 40s was that the long crankshaft became easier to bend as engines became more powerful. Before WWI, luxury makes used huge, low rpm 6s, except Cadillac, which went directly from 4s to V8s in 1915.
    That long(er) crankshaft has a long way to transmit power to the output shaft at the rear of the engine when that No. 1 cylinder fires. It's roughly half as long in a V6 configuration.
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    Re: What’s Old Is New Again – The Return Of The Inline-Six

    Quote Originally Posted by 09W View Post
    Looking forward to the engineering solutions OEMs employ putting a transverse I6 in FWD models.
    It's been done many times.

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