Why every automaker is quietly bringing back the inline-six engine
carbuzz.com

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31 points

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teleforce

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4 days ago

54 comments

smackeyacky ・ 3 hours ago

Seems weird. The I6 has a few packaging issues that made them unpopular in the 1980s when front drive vehicles became the standard.

Australia was awash in I6 motors, from the GM Holden motors, the Ford Falcon engine and the Chrysler slant 6 that got replaced by a locally developed version of a Chrysler 6 that was never finished by the US corp. they were all boring, mostly durable, mostly reliable engines for a family car.

Even BMC/Leyland had one. Uniquely they fitted it across the chassis of a land crab derived vehicle which showed why the I6 was ill suited to being packaged as anything other than in line with a rear drive drivetrain.

The V6 fits better in front drive cars for obvious reasons.

Hybrid cars change the equation somewhat, the skateboard chassis doesn’t seem all that suited to an I6 but here we are.

Chrysler have unfortunately found out that no matter how good you make one, customers still want a V8 and I concur.

  • Scramblejams ・ 2 hours ago

    Upsides are that they're both first- and second-order naturally balanced, requiring no balance shafts, which reduces weight and makes them very low vibration. I keep waiting for someone to come up with a lightweight, turbonormalized straight six that runs on Jet A to replace old turboprop engines on aircraft, but I digress...

    • GenerWork ・ 2 hours ago

      Question about that, wouldn't packaging be an issue unless you really shrunk the engine size? I thought that's what makes LS swaps into planes so interesting because you get a fair amount of power in a small package.

  • thinkling ・ 2 hours ago

    I don't think hybrids use skateboard designs the way EVs do? The battery for a hybrid is so much smaller, they usually steal space under the rear seat and/or in the trunk afaik.

  • MindSpunk ・ 2 hours ago

    Toyota with the G family and JZ family + Nissan with the RB family too. They were prolific in RWD cars.

    Daewoo put one in a FWD car in the mid 2000s for some reason too.

dzonga ・ 3 days ago

in the wild Inline 6 (I6) engines have proved reliable and just going on regular maintenance

B58 (BMW) is super reliable & high performance

same as the I6 used in certain landcruisers & other Toyota cars etc

though now of course - with super cheap solar etc - if you can go electric go electric but if you've to buy an ICE car - yeah buy an I6 - fuel efficient & performance & reliable

  • mathstuf ・ 2 hours ago

    I had an '89 Cherokee to 235k and sold it for ~60% of my purchse price after 6 years after garages only quoted insanity for the smallest things (Dad is a mechanic, but the commute there for repairs isn't feasible on the regular and apartment living is not conducive to the required garage/tools).

    Dad has seen AMC I-6s go 400k before the transmission died and ended its run.

    • sejje ・ 2 hours ago

      One of my old cars was a 1996 XJ (Cherokee), 4.0, and I sold it with 319,000 miles.

      I still see it around town from time to time, must have 360 on it now. Original engine and as far as I know, transmission as well.

      I ran it out of oil once without damaging it.

      Since then, I bought two inline-6 Ford F150s from the mid-90s. I plan on running them forever. I bought two so I can learn to work on them, and have a backup to drive. Both manual, as well.

      Jeep XJs from the 90s are still great cars to buy, so are the fords from that era (all the engines are reliable, but the I6 is starting to have a cult following online). I was working on that Jeep before I had any mechanical experience at all. It never failed to start.

    • RickJWagner ・ an hour ago

      I had an AMC with the 232 inline 6. Wonderful engine.

  • jcgrillo ・ 2 hours ago

    From Toyota there are many greats: 1FZ-FE, 1HZ, 1HD-FT, 12H-T, etc

    The Cummins 5.9L is excellent, particularly the 12 valve with P7100 pump. Awesome low end torque.

    From Mercedes the M104 and OM606 are phenomenal. Powerful, efficient, incredibly reliable. The only drawback is the aging engine management software is not very well supported by aftermarket code readers anymore. In the case of an OM606 you can fix this by deleting the ECU entirely and installing an M pump from an OM603, or replacing the ECU with a DSL-1 standalone unit.

vr46 ・ 2 hours ago

Love me a straight-six.

Why anyone thought "inline" was a better prefix, I have no idea.

Smooth, and sound great.

  • sejje ・ an hour ago

    I have two; I don't think they sound great. My F150s sound like tractors. Drive like one, too--you never have to go over 2,000 rpms if you don't care to, even pulling a load. Max torque around 1800 RPMs IIRC.

freetime2 ・ 3 hours ago

The logical, socially-conscious side of my brain can't wait to see 6 cylinder engines go the way of the v8. Four cylinders and a hybrid system ought to be able to generate enough torque for just about anyone (except maybe heavy-duty hauling?). And the future is of course BEV.

But have to admit there is a part of me that would really love to drive something like the BMW M340i [1]. And the gas mileage (26/33 MPG) isn't even too bad.

[1] https://youtu.be/kr-h9T42NAI?si=IZaDC9UqAsUtjQN9

  • gopalv ・ 2 hours ago

    > the future is of course BEV

    That's probably the reason - we only need dressage horses and pure bloods now that the real draft horse is getting put to pasture.

    These are no longer workhorses.

    Six cylinders are the smoothest engines out there.

    Honda used to have a 1L 6 cylinder engine for their bikes - the Gold wing has a 6 cylinder still.

    The perimeter of the piston goes down in relation to its area (& multiplied by BMEP) when the radius goes up - looking at you Africa Twin.

    The perimeter is where the unburnt fuel lives and gets caught up in the emission rules. So fewer larger cylinders is better according to EPA - 500cc each, maybe.

    If we're only going to have hobby vehicles with internal combustion, then a six cylinder or doubling up to a v-12 makes sense.

    They're toys for the weekend, not to put a 100k miles on it.

    • linsomniac ・ 2 hours ago

      >Six cylinders are the smoothest engines out there.

      I dunno man, have you ever driven a rotary? The design has a lot of problems, but smoothness isn't one of them...

    • RickJWagner ・ an hour ago

      My older brother had a mighty CBX. Smooth as silk, and very fast. Carburetor synchronization was troubling!

  • singleshot_ ・ 2 hours ago

    > can't wait to see 6 cylinder engines go the way of the v8.

    You want to stuff an in-line six in every race car, buggy, and Jeep that you see, with a supercharger slapped on top? Why not just go with an LS?

  • a_t48 ・ 2 hours ago

    Even 4 cylinders and a turbo (like my GLI) are plenty fun. I’m tire grip limited as it is, but it probably keeps me out of trouble, as tempting as something with more pep is.

    • freetime2 ・ an hour ago

      Yup I imagine the vast majority of car "enthusiasts" out there wouldn't be able to beat the Golf R Nurburgring lap record of 7:47 [1] in any car of their choosing.

      [1] https://www.youtube.com/watch?v=gt9l4NwHB8s

      • 7speter ・ 39 minutes ago

        In a lot of cases they don’t have to worry about caked on burnt oil lining critical passages of their engines, either.

tibbydudeza ・ 3 days ago

Well for Stellantis their fans rather want the Hemi V8 back, but they are offering a turbo charged inline 6 (Hurricane).

Badging a Mercedes as an AMG and asking the price for it and you just fit turbos on a 4 cylinder.

  • MindSpunk ・ 2 hours ago

    fwiw, the M139 engine they're putting on those AMGs is completely insane.

    It's a production 2.0L 4-cylinder engine making (in the most powerful config) 350kw. From the factory. Insane.

  • bluedino ・ 2 hours ago

    Ford F150 buyers quickly came around to the turbo V6 instead of the V8. I wonder if the Ram buyers will as well.

bluedino ・ 2 hours ago

> Inline-sixes also tend to have more low-end torque as their balanced design allows for a longer stroke, which promotes low-rev performance.

Automotive myths that won't die. 'Stroke' doesn't make more low end power than bore, displacement is displacement.

  • theodric ・ 2 hours ago

    Longer stroke provides a greater lever arm on the crankshaft, allowing the same combustion force to generate more torque during the power stroke. What's your counter-argument?

    • bluedino ・ 2 hours ago

      That sounds fantastic but it means nothing in practice. It's like something you'd hear in a "Engineering Explained" video, but with no real-world application. There's so much more that goes into an engine that it doesn't matter.

      Again, it's a myth.

      Similarly, there was always the debate over rod length (in the same displacement engines). You use the same crankshaft but the piston has the wrist pin located higher. The longer rod was always supposed to make "more torque" because of the angle but that ended up not being the case.

      You can verify this buy putting engines together with different bores and strokes that are roughly equal displacements, and with the same heads/cam on them, they will make identical power. Picture something like a 3.50" bore and 4.00" stroke, and vice versa. Look up someone like Richard Holdener on YouTube for actual data. Displacement is displacement, it doesn't really matter how you make it.

      Bore is what would make you more power after a certain point, anyway. You get more surface area to fit larger valves, etc. But again, using the same heads (that aren't shrouding the smaller bores), either combination of bore/stroke will make the same power throughout the rev range.

      Then you get into things like piston speed and all that but none of that matters unless you're talking about a race engine. And when you are, they'll just rebuild it more often so they don't care how long it lasts.

      Here's another read:

      https://rehermorrison.com/tech-talk-53-big-bore-or-long-stro...

      • unclad5968 ・ 2 hours ago
        ・ 2 more

        > Displacement is displacement, it doesn't really matter how you make it.

        If this were the case wouldnt all similar displacement engines have the same torque curve?

        • bluedino ・ an hour ago

          If you could fit the same intake manifold, cylinder head, and camshaft on them. There's things other than displacement that determine the shape of the torque curve.

          Compare a Suzuki G13B 1300 vs a Suzuki Hayabusa 1300 for example.

tim333 ・ 3 days ago

In europe inline-fours are more popular. Cheaper and less fuel.

  • SR2Z ・ 2 hours ago

    Even in the US, I4 engines are by far the most popular. Most consumer cars are built for fuel economy with the one notable exception being the suburban tacticool pickup truck, which are often modded to burn MORE fuel.

    It does not hurt that you can easily get 200+ horsepower from the factory with one, either. My car is a series hybrid with an Atkinson-cycle I4 but it still bursts to 200hp because it's a hybrid.

  • rconti ・ 2 hours ago

    The inline four has largely converged around a 2.0L displacement with an equal bore and stroke. IIRC, it's fairly optimal from a performance and thermodynamic efficiency standpoint.

  • cucumber3732842 ・ 3 hours ago

    Europe has stupid displacement taxes so they'll make some high strung 0.9L turbo 3/4cyl with all the technology that gets .01mpg better MPG than a ~2L engine while taking twice as much $$ in service to make it to any given milage.

    IDK why they don't just tax the actual fuel used like the rest of the world (not that they don't do that).

    • ahartmetz ・ an hour ago

      I'm not sure if displacement taxes still exist, but direct car taxes are fairly low in any case (like 200€ per year or so for an average car in Germany?). Most of the tax is paid through the fuel. The actual reason for downsizing (small turbo engines) is that they consume less fuel under light load, which is where car engines spend most of their time. It's not great for longevity though. Car engines had become more and more reliable over time apart from a few teething troubles of occasional new technologies, now some people say it's trending down due to downsizing.

    • therouwboat ・ 2 hours ago

      In my country its based on emissions, 1.6l 4 cyl 140g/km co2 is ~150e, 3 litre V6 300g/km ~500e.

  • jfengel ・ 2 days ago

    Americans like their cars enormous and heavy.

    • sejje ・ an hour ago

      Like electric vehicles?

znkynz ・ 3 hours ago

Buggy makers building fancier sounding whips.

theodric ・ 2 hours ago

I love a straight-6 so much that I drive a car that uses two of them joined at the crankshaft! Each I6 has its own ECU and is entirely unaware of the other. Crude, but very smooth nonetheless.

  • CuriousRose ・ 2 hours ago

    A fellow 850c/s/i enjoyer?

  • ebbi ・ 2 hours ago

    Need more details of this beast!

  • GenerWork ・ 2 hours ago

    Older BMW 7 series?

  • jcgrillo ・ 2 hours ago

    this thread is worthless without pics ;)

RickJWagner ・ an hour ago

My first car, a 1965 Rambler, had the venerable AMC 232 cubic inch inline 6. It had decent torque, was thrifty, and proved nearly impossible to kill. Best of all, in the mid sized Rambler the I6 left enough room in the engine bay that I could stand beside the engine— under the hood- to work on things.

Spark plug replacement, points change, air filter… even things like water pumps and carburetor were trivial to work on.

Today’s cars are better in almost every way, but I sure loved the simplicity of that engine.

Also: I’m a little surprised the article didn’t make mention of a similar ( but slightly different ) engine. The mighty Mopar slant 6, which is legendary for durability. Maybe we’ll get a newer one of those, too!

jcgrillo ・ 2 hours ago

There's potentially an even better option than the I6 layout: opposed piston I3 2 stroke. Same number of power pulses per rev as I6 4 stroke, no valves, no cylinder heads. It seems that these guys solved the oil loss problem and by using 2 injectors and some awesome combustion modeling they've been able to beat emissions standards without after treatment: https://achatespower.com

  • wepple ・ an hour ago

    This has been done before; heat and having two crankshafts kinda kills it

    • jcgrillo ・ an hour ago

      It's been done many times before, quite successfully. The Napier Deltic (3 crankshafts!) and Junkers Jumo are two examples. The Commer Knocker is another (which had only one crankshaft I believe). Two crankshafts makes the engine slightly taller, but not egregiously so.

      I'd be curious to know more about the heat problem you've mentioned. Naively, there should be much less waste heat to dispose of due to the fact that the same cylinder volume is doing twice the work.

dboreham ・ 2 hours ago

My TR6 is happy to see this.

1970-01-01 ・ 3 hours ago

Yet Another Bad Idea. The only engine that makes sense is a small generator married to an EREV. Everything else will be dead in 10 years.

  • freetime2 ・ 2 hours ago

    For buyers today that may actually mean less depreciation as six cylinder engines become harder and harder to find. But yeah I'm sure automakers can see the writing on the wall.