How long can the BMW straight-six last?

Interesting | December 31st, 2015 by 15
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BMW has a long standing tradition of making six-cylinder engines with their cylinders all in a line. The I6 engine was something that several automakers …

BMW has a long standing tradition of making six-cylinder engines with their cylinders all in a line. The I6 engine was something that several automakers used decades ago. Companies like Ford, Mercedes-Benz and Jeep made many I6 engines along side BMW up until about the mid-eighties. In fact, Jeep used a 4.0 liter I6 engine in the Cherokee up until 2001. But BMW is currently the only automaker to use the long-block engine and it’s something worth applauding. I think that the only other car manufacturer to be so tied to an engine architecture would be Porsche and its flat-six engine.

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BMW N55 straight-six engine

The inline-six engine has all but died out, aside from the Bavarians, though. Packaging and cost have brought about the mass use of V6 engines to replace the I6, as V6’s are more cost effective and allow for better packaging which also helps with crash protection. So it’s understandable why so many automakers switch to bent-sixes. This only makes BMW’s stubborn pursuit of the straight-six more admirable, much like Porsche’s stubborn pursuit of its rear-engine design. The straight-six has become a calling card of BMW, a flag that fans wave proudly. But, unfortunately, it’s unknown how much longer BMW can keep making them.

The pursuit of downsizing and turbocharging, for the sake of emissions and fuel economy, has reached the furthest depths of the automotive world, infecting even Ferrari and McLaren. So naturally, BMW has fallen victim to this necessary trend. With that, BMW has made the move to four-cylinder turbocharged engines in almost all of its entry-level vehicles. The 2 Series, 3 Series, 5 Series and Z4 all have four-bangers under the hood in their lowest-spec models. Even the X1 and X3 SUVs have done the same. So it’s clear that more and more four-cylinder engines are coming.

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BMW N20 TwinPower Turbocharged four-cylinder engine

This isn’t such a bad thing, as BMW actually built its reputation with four-cylinder engines. Two of the most iconic cars to ever wear the roundel, the BMW 2002 and E30 M3, used four-cylinder engines. Even BMW’s headquarters, nicknamed the “Vierzylinder” is in the shape of four cylinders to represent the importance of the engine to BMW. So it’s not as is four-cylinder engines would be bad in a BMW. But there’s just something about the straight-six engine that feels more BMW. Maybe its our age, as most of use look at the I6 engine as the icon of BMW. Cars like the E46 BMW M3 or BMW M1 come to mind.

Granted, BMW will be able to continue its straight-six engines for some time, still. BMW did make the switch back to the I6 in the new M3/M4. Plus, its turbocharged I6 engines are some of the most efficient six-cylinder engines on the market, if not the most efficient. Hell, the 335i is more efficient than many four-cylinder engines on the market. And even as restrictions grow tighter, BMW can continue to make straight-sixes, just smaller. It wasn’t that long ago that BMW sold a 2.5 liter straight-six engine in the BMW 5 Series. So BMW can continue to use the engine for a bit longer. But how much longer?

BMW 2002

Four-cylinder BMW 2002

Even if BMW can make six-cylinder engines that are incredibly efficient and match the stricter-growing emissions regulations, many customers will feel as if they simply don’t want six-cylinder engines in the future and want to downsize. It’s inevitable that one day the straight-six engine will die. We, as fans, won’t be happy that day and will mourn the death of one of the greatest engine architectures of all time. But when it does die, at least we can take solace in the fact that the four-cylinder engine is every bit as important to BMW’s history as the straight-six.

15 responses to “How long can the BMW straight-six last?”

  1. Mike N. says:

    Mercedes is going back to straight sixes with the new E or shortly thereafter. I don’t think that engine style is going anywhere. The 90 degree V6 was always a cost saving compromise.

  2. IceDree says:

    Mercedes is going back to Straight6 with the new E, word is its gonna be a 2.7 Turbo… Luckily, we’ll find out soon … NAIAS is less than 2 weeks away.

    I don’t think BMW is going to ditch the I6 anytime soon, it fits in almost all their cars & they designed their new I6 to have as much commonalty as possible with their next crop of engines … So its a long term thing.

    Plus, the I6 is very popular choice in the X5, X6 & 7er.

  3. Mark Tucker says:

    First the reason why you see all those V6’s is the need to package a six cylinder engine into a front wheel drive package. The turbo four is displacing this format. Thus the V6 is now an endangered species.
    BMW’s preference for the Inline six is linked to the cost advantage of be able to produce a range of inline engines on a common production line and a preference for rear wheel drive. A cost advantage that is as important to today, as it was thirty years ago. Thus my prediction is that the Inline six will live on as long as BMW produces an Inline three or four.
    We also hear rumours that Jaguars next six will be an inline six, driven by the same need to produce it on a common production line with its new inline four. As suggested by others Mercedes appears to also understand the capital efficiency that supports the inline six format.
    The bottom line, the inline six is safe for the next 15-20 years.
    But what if BMW had choose between Inline six or a V8 as a stand alone hero engine in a future where the only ICE’s are found in M performance models? For some manufactures this choice will be easy, the V8 will be the only acceptable option. Consider GM, why would they pick anything other than a V8? Would BMW be forced to follow to compete?

    • maz2331 says:

      The I6 has inherent balance and torque advantages over the V6 or the I4. It is as refined as a V8, and often just as powerful, while not being a total gas guzzler.

      • Mark Tucker says:

        I agree that an I6 is a smoother configuration than a V6 or an I4 and also ultimately more powerful. The I4 actually has the torque advantage due to a smaller rotating mass, the I6 usually winning at the power battle due to superior breathing, and sounding better doing it. The old BMW naturally aspirated, small capacity sixes where well known for having not much down low but having a great top end.

  4. Pictor says:

    1) MB is going back to I6 engines.

    2) V6 was a compromise to build a smaller package that worked in a transverse engine FWD layout.
    3) The term “long-block” engine doesn’t mean what you think it means.

  5. Kommodore says:

    The first image is an N54, not an N55.

  6. luedriver says:

    this shouldn’t be an issue, every company makes what its good at, if bmw, or anyone else wants to make an engine a specific kind of way, let them, its easier to improve upon something you know than to try something different, by the way, all this talk of downsizing and bmw has yet to make a small 2 seater roadster with a motorbike engine at the back, why not?

  7. Darko says:

    My uncle owns m52b25 E39. Engine was rebuilt last year, still pulls strong at 430k km and these are known to run 500 even 600k, very durable and reliable…

  8. Nedlands says:

    Ford Australia still sells a 4 litre straight 6 in the Falcon. This motor is about 40 yrs old.

  9. 3223 says:

    This article can be directed to any and all engine configurations. The v8, the v10 (which is much rarer!) and even the v12.

    Strictly speaking it’s not so much the death of the inline 6, more like the pending death of the internal combustion engine as a whole as electricity becomes more of the ‘in thing’.

    Also, the death of driving pleasure as cars start to become autonomous. That’s the sign of the times….

  10. maz2331 says:

    The I-6 will never truly die. It has too many advantages in balance, smoothness, and torque versus a 4-banger. Any 4 putting out 200+ HP will eventually shake itself to death by beating the bearings on the crank and counterbalance shafts into oblivion, whereas an I-6 will spread the load among 7 main bearings and last forever.

  11. David Luke says:

    i love my straight 6, i got the 2.5 bmw straight 6. runs strong as hell. hella quick

  12. J W says:

    Volvo xc60 transverse inline 6 engine, turbo 3 liter. Rented one of these very nice

  13. Gregory Moore says:

    Sorry to have to correct you, but at the time of writing this, Australia still had a very successful inline 6 still in production. Look up “Ford Barra engine”. It can achieve over 200kW with premium fuel in a standard family car. The turbo variant made up to 310 kW. They stopped producing them in late 2016 but still sell this engine for industrial applications.

    Australia has had a long-term love of the inline 6 since the 1940s. Holden, the Aussie GM subsidiary, started with its 138 “grey” motor, then the Falcon came along in 1961 with its 144 & 170 sixes. Holden then released the “red” motor in 1964 and both of these continued to be best sellers for many years after. The Falcon continued with the I-6 right until the end.

    Chrysler Australia also built their own inline: the 215/245/265 Hemi. In its highest performance version, it made 302 hp with triple Webers. It was the most powerful 6-cyl engine in the world for many years after.

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