By on November 28, 2016

Jaguar straight 6 engine

As a parent of two young children, I watch a lot of movies at home. Most of the blockbuster movies I’ve watched this year are remakes. This month alone, I watched Ghostbusters, Star Trek Beyond, and Star Wars: The Force Awakens. All three are part of franchises that died a decade (or more) ago and have been reborn successfully in 2016.

In the same way, inline-six engines have returned to Mercedes-Benz after nearly a 20 year hiatus in North America.

Why are straight six engines making a comeback?

Guess who’s back, back again?

The straight six is the ideal six cylinder engine from a simplicity, smoothness, and efficiency standpoint.

The smoothness and balance come from the engine’s configuration. The front three cylinders and rear three cylinders are mirror images and move in offset pairs. This allows for perfect primary and secondary balance without power-robbing balance shafts, and allows the engine to be much smoother than a V6 or inline four, especially in high-rev applications.

Inline_6_Cylinder_with_firing_order_1-5-3-6-2-4

In addition, because of the inline layout, only a single set of camshafts is required for the valvetrain, compared to two sets for multi-bank V6 and V8 engines.

The design’s simplicity has driven the use of inline sixes for larger vehicles such as monstrous Caterpillar earth movers and even mammoth ships.

Why are (almost) all six cylinder engines V6?

The V6 engine is the engine of accountants; it was developed for packaging and modular manufacturing. In every other area, it has more vibration, a more expensive valvetrain, complexity, and worse exhaust noise than the inline six.

In the 1990s, Daimler switched from inline sixes to V6s because of cost; the new V6 configuration allowed the engine to share architecture with its V8, reducing overall development and manufacturing costs.

Other car manufacturers adopted V6s for similar reasons. In the 1980s, there was a push to adopt front-wheel drive, especially for midsize and compact cars to maximize interior room and save on cost. The other trend was the downsizing of engines; four-cylinders were substituting six-cylinders as base engines, while six-cylinder engines were substituting V8s. In addition, it’s almost impossible to fit an inline-six into the engine bay of a midsize car. The length of the motor makes it either too wide or too long, depending on its orientation under the hood.

As a result, by the late ’90s, almost all car makers had switched to V6 engines for their passenger cars. Volvo was one of the rare exceptions with its 2.9-liter inline six in the S80, but it was only able to achieve this with a special gearbox. BMW is another exception, as its tradition (at least in the ’90s) dictated inline-six engines and rear-wheel drive. Furthermore, BMW’s front engine, rear-wheel-drive layout meant it had sufficient engine bay room for a longitudinally mounted inline six.

The packaging benefits of the V6 engine did come with downsides. To share engine architecture with a V8, a V6 engine needed to have a 90-degree angle between cylinder banks. This type of arrangement needed to have extra balancing shafts to neuter vibration. A 60-degree V6 was the better design from a balance standpoint, but it couldn’t share any architecture with the V8 and had to be designed separately. In addition, because of the two separate cylinder banks, there needed to be twice as many camshafts for the valvetrain as an inline engine. This lead to additional cost and complexity.

Return of the King

After more than two decades, the stars have now realigned. Now that modular inline engines are once again cost feasible, the technically superior inline six configuration is once again the engine of choice.

In recent years, fuel economy requirements have led to engine sizes and the reduction of the number of cylinders in engines. Turbo inline-four engines are replacing V6s; turbo sixes are replacing V8s.

OEMs can now make a modular line of inline three, four and six cylinder engines on the same manufacturing line and share development costs. They also benefit from reduced valvetrain cost for an inline engine compared to a V6.

We are seeing this resurgence this year from several European manufacturers. Mercedes-Benz is abandoning its V6 and replacing it with an inline six that can also share architecture with its inline four engines. Jaguar Land Rover is rumored to be developing an inline six engine based on its Ingenium line of four-cylinder engines. For BMW, the inline six engine is here to stay for the same reasons. While there are still some BMWs available with V8s, the majority are based on its new modular turbocharged inline three, four and six cylinder engines.

It would not be surprising to see a similar revival from Japanese and American manufacturers. For example, Toyota and Nissan had turbocharged six cylinder engines in their lineups until the late ’90s. With the lack of market for new V8 engines, the next generation of engines could be developed on an inline platform.

Get the latest TTAC e-Newsletter!

Recommended

163 Comments on “The Straight Six is the Best Six — And It’s Making a Comeback...”


  • avatar
    Land Ark

    Wow, that’s funny. I tried posting a comment last week wondering if there were any straight sixes left in the market for mass produced cars and it got eaten somehow.

    My only experience with one is the IS300 I fixed up for my mom last year and all I can say is that I am 100% sold on it. It is so smooth and a dream to work on.
    I for one welcome our straight six overlords.

  • avatar
    Carlson Fan

    An I6 is a great engine in a truck due to all the torque they produce down low. Add a turbo and it would be phenomenal. Exactly why people love the Cummins in the HD RAMs.

    • 0 avatar
      JimZ

      there’s nothing inherent in the I6 design which gives it “all the torques down low.” truck I6s aren’t “great at low end torque” as much as they just “suck at making horsepower.” Even the legendary Ford 300 I6 had less torque than the contemporary 302 V8, and WAY less horsepower.

      • 0 avatar
        Carlson Fan

        An inline vs V configuration gives better torque at lower RPMs.. Who cares if a 302 made more torque than an I6 if you needed to wring another 2K RPM out of it to do it. I’ve towed with I6 powered vehicles and absolutely they are excellent for towing so you don’t know WTF your talking about.

        • 0 avatar
          JimZ

          “An inline vs V configuration gives better torque at lower RPMs.. ”

          just stating it again as though it was fact doesn’t make it right.

          “Who cares if a 302 made more torque than an I6 if you needed to wring another 2K RPM out of it to do it. ”

          the torque peak of the 302 was only a couple of hundred RPM higher.

          “so you don’t know WTF your talking about.”

          Yes I do. if you’re going to tell me I don’t know what I’m talking about, show me some evidence instead of just sh*tting out whatever “truthiness” you’ve been force-fed.

          If the only reason you “know” something is because it’s something “everyone knows,” you don’t actually know it.

          • 0 avatar
            Carlson Fan

            “If the only reason you “know” something is because it’s something “everyone knows,” you don’t actually know it.”

            My “know” comes from actual experience. I’ve towed roughly the same load in an F150 with both a 302 and the 300 I6. How about you? The 302 may get it from 0-60 MPH faster but the I6 does it with less effort and drama. More grunt down low, just what you want in a truck, Every PU & SUV I’ve ever towed with the had an I6 was excellent. The I6 Cummins is a better truck engine than either V8 diesels in the Ford or GM trucks. Too bad it’s wrapped by RAM. And I’ve towed with all of those too.

          • 0 avatar
            JimZ

            *That* is your evidence?

        • 0 avatar
          stuki

          “An inline vs V configuration gives better torque at lower RPMs.. ”

          Why? Unless there are some limitations of stroke length imposed by a V-layout, it would seem the shorter, hence less bendy, crank and block of a V could stand up to higher peak torque. Assuming someone were to arrange a world championship in peak torque production at 2000rpm for an X liter 6 cylinder ICE or something.

          Just speculating, but I’d suggest it’s more likely that one reason to go to a V6, is to be able to build lighter internals than can be done when confined to a long inline block. In order to better tap into high rpm operation. So that the only I6s left, are the ones tuned for low end, while the V6s are tuned for midrange/top end.

          • 0 avatar
            JimZ

            As I posted below, it’s easier to make a very under-square (long stroke) engine with an in-line block by “flaring” the bottom end for clearance from the con-rod swing. But doing a long stroke engine doesn’t really get you “more torque,” it gets you less horsepower because a longer stroke (all else equal) brings higher peak piston speed for a given RPM, lowering your redline. Also, for a given displacement, a longer stroke means a smaller bore thus smaller valves, limiting horsepower potential further.

        • 0 avatar
          Silence

          Cylinder size, cylinder pressure, and crankpin offset determine torque. Aside from wonky firing intervals, cylinders don’t care if they are in a V or inline configuration.

          • 0 avatar
            Big Al from Oz

            Silence,
            Another significant factor affecting torque and powerbands is the squareness of an engine.

            Over square engine have a broader and flatter powerband and vice versa for under square engines.

            Variable valve timiming can alter this, but the effects of engine squareness is always present.

        • 0 avatar
          Kyree S. Williams

          Let’s be civilized, please.

    • 0 avatar
      RobertRyan

      @Carlson Fan
      Depends on the other aspects of the engine. I know the turbo charged version of the Barra, gets 430hp and 420lbs ft of torque. That comes in at 1800rpm and that is a very flat torque curve.Last version had 470lbs ft for roughly 10 seconds

  • avatar
    JimZ

    “OEMs can now make a modular line of inline three, four and six cylinder engines on the same manufacturing line and share development costs. They also benefit from reduced valvetrain cost for an inline engine compared to a V6.”

    this isn’t anything new; remember the GM Atlas engine family? 4, 5, and 6 cylinders on a common architecture.

    besides, I wouldn’t get ahead of yourself here. you’re looking at a few engines from a couple of luxury car makers who see the inline-six as part of their “heritage.” 60° V6s are “good enough” for everyone else. The “technical superiority” of the I6 is only interesting to car geeks.

    • 0 avatar
      ToddAtlasF1

      I recall that one driver of the abandonment of I6s is that I6s are hard to package appropriately for crash testing. When mounted longitudinally, their length and height is a liability in both pedestrian and barrier crashes.

      • 0 avatar
        Windy

        When was the first Slant 6 packaging to reduce the height factor as a packaging problem? were any of the pre war cars using a slant 6? I know M-Benz in the early 50s used a slant 6, 3 liter direct fuel injected dry sump lubricated engine to get a low profile in the 300SL gullwing but I am fairly sure that it was not first.

        • 0 avatar
          ToddAtlasF1

          Slanting the engine helps with the height issue, but it’s still a big long block waiting to transfer the energy of an impact into the passenger compartment.

          • 0 avatar
            dukeisduke

            M-B used to compensate by designing the engine and transmission mounts on the I6 to force the engine to angle downward at the rear as it was pushed rearward in a collision. This was to keep the powertrain from intruding into the passenger compartment.

          • 0 avatar
            ExPatBrit

            Todd is correct, it’s all about the crash structure.

            Largish RWD drive cars/ trucks with longish engine bays.

            Small niche in most of the world.

          • 0 avatar
            Jeremiah Mckenna

            That was true of older designs. Now there are engines that actually fall out of and under the car during extreme front end collisions. That, along with impact energy absorbing materials and crumple zones and better seat belts and of course, SRS, today’s cars can have the I6 and the passenger compartments will still fair quite well in a major front end collision.

      • 0 avatar
        stuntmonkey

        Send the IIHS small offset test of the current BMW 3series…. I gets a marginal rating. From the outside the cabin looks great, not much deformation at the top or side, but significant footwell intrusion into the driver’s legs. Granted not strictly a i6 car, but packed to accept a 6 at the highest trim level.

        • 0 avatar
          ToddAtlasF1

          Unfortunately, the ghost of BMW is the only company attempting to certify an I6 passenger car these days. The issue might not be insurmountable for one of the engineering-oriented carmakers, but Toyota pulled the plug on its I6 a while ago. Mercedes-Benz cited the crash testing reasons when they were rationalizing their dreadful 3-valve per-cylinder, twin-plug, balance shaft V6s replacing an obviously-superior family of I6s. I assumed there was some truth when Lexus similarly started putting minivan motors in IS and GS sedans.

          • 0 avatar
            threeer

            And I deeply miss the I6 from my old 325is (as does my wife!). I always laugh when I see a Craigslist ad now for an older 3-series that lists “V6” as the engine!

          • 0 avatar
            Featherston

            @ ToddAtlasF1 – In fairness to Lexus, the GR is a damned fine minivan motor. :-)

            Whatever balance shaft witchcraft they’re doing to offset the rocking motion is working really well.

          • 0 avatar
            MBella

            That dreadful engine exceeds torque and horsepower figures of inline engine it replaced. It also doesn’t have head gasket issues. The 112 V6 is one of the most reliable engines ever produced. Their only real issue is leaky valve covers and a faulty Bosch crank sensor. (Replaced by a Hella unit that is reliable and affordable) It is a very difficult engine to kill, even when people try.

  • avatar
    PrincipalDan

    I welcome this news. I’m still mad that the Atlas I-6 never made it under the hood of GMs base model half ton trucks.

    • 0 avatar
      PrincipalDan

      If someone could get me out of moderation purgatory, that’d be great…

    • 0 avatar
      gtemnykh

      It would have been neat to see some sort of lower-cost RWD Caprice/Holden type sedan with the 4.2 Atlas under the hood. And yes to putting that motor into half tons (and heck into the new Colorado while we’re dreaming). I remember getting a ride in a coworker’s Trailblazer with the 4.2. Horrid interior but man that motor ripped.

      • 0 avatar
        PrincipalDan

        In 2006 I bought a 2004 F150 with the 4.6 V8, I was open to a used Chevy or GMC but didn’t want the old Vortec 4.3 if I ended up with a base version. (I like my trucks with very few options.) I lucked into the F150 and the only real options it has is V8 and automatic.

        If GM had offered the I6 that would have been something special and I would have searched hard for one.

        I knew someone who bought a Trailblazer based on their love of the sounds the engine made.

    • 0 avatar
      bumpy ii

      Typical old GM think: they never designed the Atlas to fit in anything other than the TrailBlazer. And it would have been an expensive replacement for the cheap-as-dirt 4.3L, which was the last remnant of the traditional SBC architecture.

      • 0 avatar
        PrincipalDan

        @bumpy ii, well duh. :-)

        I was just sad that I couldn’t get an obviously superior (to the 3/4 of a SBC = 4.3) engine in a vehicle that from a mental standpoint was a natural fit.

        Straight 6 and a 1/2 ton pickup go together like peanut butter and jelly.

      • 0 avatar
        davefromcalgary

        I love the size of a last gen Colorado crew, but the I5s are slugs. I’m actually quite taken with the 5.3L equipped ones though. Got a few saved in classifieds.

        • 0 avatar
          gtemnykh

          dave I’m the same way, they are rather aesthetically pleasing. I’ve been enamored with them ever since my Mexican coworker helped my group evacuate out of the path of a hurricane in his Z71 quad cab (company truck). Never mind that the dash was a Christmas tree of lights and the 4wd actuation was out of commission (silly push button things on dash). Interior is comically bad, but again what do you want from a GM small truck. I bet they’re quite peppy with the 5.3L! Resale on them is really eyebrow raising as well.

          • 0 avatar
            CoreyDL

            “(silly push button things on dash)”

            Does he have the red light, like is a common Tahoe issue where it’ll default to RWD?

  • avatar
    ajla

    I’m fine with this. Especially with Jaguar and Mercedes. Although I hope Alfa, Honda/Acura, and Buick keep the V6.
    ———————-
    “only a single set of camshafts is required for the valvetrain, compared to two sets for multi-bank V6 and V8 engines.”

    Well… Not nesecarily.

    • 0 avatar
      davefromcalgary

      Essentially since the Church approved OHV motor is almost extinct. :-(

      OHV for liiife!

      • 0 avatar
        PrincipalDan

        @ajla, did you ever manage to get a vehicle with the GM 3.9 V6 just to sample the last gasp of the automotive OHV V6 at GM?

        I’d be tempted by a loaded-up well kept Lucerne with the 3.9 especially since the Northstar option didn’t really make that much more power.

        • 0 avatar
          28-Cars-Later

          Like the LS4, the 3.9 likes to chew threw the 4T65-E (at least in commercial service). For this transaxle, its 3800 or less if you’re looking to see a long life.

          • 0 avatar
            gtemnykh

            28 cars I don’t see how the 3.9L would put any appreciable amount more stress on the transmission. I think the “commercial service” aspect is key: cops wringing these things out puts the kibosh on the transmission. Just the AFM issues and mediocre mpg would put me off of the 3.9L. 3800 or bust.

          • 0 avatar
            28-Cars-Later

            The 3.9 puts out slightly more torque at peak and about 40 more hp (240 hp (179 kW) and 240 lb·ft (325 N·m) torque per wiki). I suppose this is enough to cause issues commercially.

            “3800 or bust.”

            Thou has found faith!

        • 0 avatar
          ajla

          No, I’ve never bought a 3900 car. I’ve driven a few. They’re okay but aren’t as tenacious as the 3.6L or as comfortable and nostalgic as the 3800. I think the only one with the 3900 I’d go for today is a Monte Carlo LTZ just for the rarity of it. Although right now I’m semi-seriously looking to replace my Seville with a GTP Comp-G.

          I did own a Lucerne, but it was a 3800 powered one. Personally I prefer the Park Avenue to it. The Park is a fun old man car, the Lucerne is a boring old man car.

          The OHV V6 banner is still being carried by the Silverado and Sierra. It’s unlikely that I’ll ever buy a truck without a major lifestyle change, but I’m glad the configuration lives on.

  • avatar
    zerofoo

    I love my Jeep 4.0L inline six. Sure – its traces its roots back to AMC in 1964 but they routinely hit 200,000 miles without much effort.

    https://en.wikipedia.org/wiki/AMC_straight-6_engine

  • avatar
    -Nate

    I6’s *do* make more torque @ lower RPM’s, if you drive them you’d know this .

    I think this is a great comeback idea .

    Make them all 12 ports so they’ll breathe properly and you’re off and running .

    Didn’t Honda make a tiny i6 racing engine in the early 1960’s ? .

    Like 250 C.C. or something absurd .

    -Nate

    • 0 avatar
      Jeff Weimer

      Honda had an inline 6 *motorcycle* – the CBX1000.

      http://www.motorcycleclassics.com/classic-japanese-motorcycles/honda-cbx-1000

    • 0 avatar
      JimZ

      “I6’s *do* make more torque @ lower RPM’s, if you drive them you’d know this .”

      wow, more proof by assertion.

      you’re taking particular engines’ overall design goals and trying to pin it on one simple characteristic (the cylinder layout.) Tell me, if I6s are so inherently torquey then why aren’t the V8 diesels from Ford and GM having any trouble matching or beating the almighty Cummins I6?

      • 0 avatar
        FormerFF

        A six cylinder engine is a six cylinder engine, its arrangement shouldn’t affect its power curve, that’s a matter of tuning. Most inline sixes have been tuned for torque because that is what was needed by the vehicles they were installed in. I suspect that is where the idea came from

      • 0 avatar
        bunkie

        I suspect that many I6 engines were long-stroke designs (necessitated by the need to use narrower pistons to minimize block length), which is why I6 engines have a reputation for torque.

        The 2.0 liter I6 in my old Triumph GT6+ was a torque monster, and it was an undersquare design.

        • 0 avatar
          BigOldChryslers

          Also, in the days of carburetors, most engines had a single carb which had to feed all the cylinders. Many I6’s have intake and exhaust ports on the same side, so the intake and exhaust runners had to avoid each other.

          Due to these criteria, the I6 intake required long runners to reach all of the cylinders. Longer intake runners move the power band lower in the RPM range. With multi-point EFI this is no longer a limitation/feature of the I6.

          • 0 avatar
            Featherston

            I know you’re specifying I6s, but my eyes are seeing “BigOldChryslers” and “long runners” and my brain is interpreting them as “Sonoramic Commando.”

      • 0 avatar
        raph

        I6’s do have an advantage with torque (all things being equal except engine configuration) IIRC its something to do with the angular displacement of the connecting rods in an in-line configuration compared to a V configuration.

        Its been a long time since I argued your same position and the other guy on the forum (CamaroZ28.com) brought his fancy spreadsheet into the argument.

        • 0 avatar
          JimZ

          Well, since I don’t know what some guy at CamaroZ28.com had on his spreadsheet, all I can say is that it sounds like you’re confusing what you *can* do in an inline-6 package with some inherent design quality of an inline-6, and that’s not the case. Theoretically, you *can* go for a longer stroke in an inline engine, it’s easier to “flare” out the bottom end of the block to give more room for the swing of the crankpins and rod ends than it is in a vee engine. but increasing the stroke has its own trade-offs, all else equal you’re increasing the crankpin-radius-to-conrod ratio which means the peak piston speed for a given RPM will be higher. Peak piston speed is a pretty hard limit if you want engine longevity, so your redline goes down the longer you make the stroke. so again, I6s got a reputation for “great torque” because so many of them have been under-square wheezers which were sh*tty at making horsepower. Their torque output just *looked* good in comparison. There is nothing (NOTHING) about putting the cylinders in-line which *inherently* gets you greater torque output. all else equal, an I6 and V6 of equal displacement and bore x stroke will perform identically. hell, Detroit Diesel had 6-71 (inline) and 6V-71 (vee) versions of the same engine, and they made the same horsepower and torque.

          • 0 avatar
            Caboose

            What about lower parasitic losses of the inline layout due to saving the rotating mass of balance shafts versus a V6 with all else equal between the two engines? Is it entirely unreasonable that the greater efficiency of the inline might be felt as “moar torkz” by the driver?

          • 0 avatar
            JimZ

            60° V6s don’t need and usually don’t have balance shafts.

          • 0 avatar
            raph

            It had nothing to do with increasing the stroke on the engine (which is mostly a moot point – when you increase the stroke, gains made by increasing the length of the lever are offset by a loss in surface area on the piston along with increased friction except as you note it alters the breathing characteristics of the engine).

            Also the reason why I said “all things being equal” (i.e.; bore, stroke, rod length and so on) the inline engine will have more torque.

            Its been a long time since I had that argument so I cant remember the exact mechanism involved except it had nothing to do with the bore and the stroke and everything to do with the length of time power was imparted to the crank in degrees of rotation.

          • 0 avatar
            JimZ

            raph,

            that still makes no sense since an I6 and a 60 degree V6 both have an even 120 degree firing interval. so- if all else is equal- there will be no difference in how either layout “imparts power to the crankshaft” thus no difference in torque characteristics.

      • 0 avatar
        RobertRyan

        @JimZ
        Try inherently smoother than a V6, potentially easier to extract more power.Torque is a not greater. Inline 6,’s have a packaging issues. Not a big deal for BMW

  • avatar
    PCP

    Opel Monza 3.0, Toyota Supra MkIV, Ford Falcon 3.9 – each one totally different from the others, but all of them absolutely great on their own thanks to an inline six. Of course the Supra was my favorite…

  • avatar
    Zackman

    I like this. I like this a lot. I want a Chevy drivetrain that is a 250 cu. in. inline 6 with a Powerglide transmission again.

    Make things simple again. I’ll drink a whole pitcher of that Kool-Aid. Life in the slow lane is a wonderful thing.

  • avatar
    Duaney

    The only advantage’s of the V-6 to the straight six is packaging, (the compact size), and fuel distribution. The fuel distribution aspect is with a carburetor, the V-6 engine can have a short, square, evenly spaced intake, better fuel distribution and more even air flow. But with port injection and computer controlled combustion, the straight six will do just fine.

    • 0 avatar
      stuntmonkey

      Also the shorter cank, less rotation inertial, freer revs.

      • 0 avatar
        bunkie

        Yeah, the longer crank is an issue. But that can be easily overcome using a two-piece block like that of the oft-maligned Northstar which has incredible crank and main bearing life as a result.

        Of interest is the Ford T-drive design of a few years back that mounted a straight 8 transversally and had the power taken off the middle of the crank. This could give the straight six a packaging advantage for RWD applications.

  • avatar
    heavy handle

    Straight 6s never got results in racing because the design inherently limits RPM and power. The crankshaft and camshafts are so long that they flex at high output levels. The only way around that is to have a power take-off in the middle of the engine (between cylinders 3 and 4), making a straight 6 from two mirrored straight 3s.

    I did like the last straight 6 M3, great car and great engine. That being said, BMW raced F1 with a straight 4 during the turbo era, not a 6.

    • 0 avatar
      jimble

      I wouldn’t say “never.” Hudson won a lot of NASCAR races with their big inline sixes back in the 50’s.

      • 0 avatar
        heavy handle

        There was indeed a period in early Nascar history when the flathead Ford was petering-out and the new OHV V8s weren’t there yet. As with the Le Mans Jags, the Hudson 6 won in spite of its engine. It had lower weight and better handling.

    • 0 avatar

      Drivers of successful C and D Type Jaguars and some Aston Martins would dispute the comment of “never got results”.

    • 0 avatar
      runs_on_h8raide

      Just an aside on the BMW 4cyl turbo…depending on what experts you talked to, it was the highest horsepower engine in F1 ever producing a staggering 1400-1500hp in qualifying trim. Those were the days!

    • 0 avatar
      davefromcalgary

      My understanding is that well designed higher output straight sixes will have N+1 main bearings, N= no cylinders. This deals with saggy cranks.

      • 0 avatar
        TonyJZX

        I think there’s a lot of provinciality here.

        The RB26 in the Skyline has an incredible, singularly unique racing record.

        The 2JZ in the Supra has a lesser record but it still is the flagwaving king of the drag racing circuit.

        These are two legendary inline sixes.

      • 0 avatar
        Bangernomist

        Not all of them. Seven main bearing cranks do pay a penalty in torsional stiffness with the extra crank throws that can impact high RPM operation. IIRC the BMW “baby six” had four main bearing cranks at least in some iterations for this reason.

    • 0 avatar
      Oosh

      Nissan Skyline dominated touring car categories wherever it competed in the 90’s.

    • 0 avatar
      Bangernomist

      The central power take-off is what Porsche did with the 917’s engine, and it wasn’t original with them. In addition to limiting the spark and timing scatter that come from driving the cam and distributor at the end of the crank, it takes advantage of a vibration node at the crank center (think standing waves) which makes it a good place to put a gear drive. I’ll bet Volvo considered the idea for their SI6 transverse six but chucked it for cost reasons. And with the reliability issues they saw with the rear-end gear drive takeoff they used, I’ll bet they regretted that choice…

  • avatar
    npaladin2000

    I wouldn’t mind seeing an I6 engine small enough for a transverse FWD/AWD configuration in a compact/midsize car or CUV. Even if you have to stagger the cylinders slightly to get it to fit, you get to ditch all the anti-vibration hardware. And you can always turbo it.

  • avatar
    SaulTigh

    The guy at my local Mercedes dealership said they were going to “all 4-cylinder” power and that there was no such thing as a “straight six” in the pipeline. This was about 6 weeks ago. I don’t know what to believe.

  • avatar
    relton

    The most efficient engine, both in terms of weight and power out, remains the 90 degree V8. Cost, and public image, keep this from being the engine of choice.

    Inline 6s have a weight penalty compared to a V8 of the same displacement. Weigh a BMW turbo 6 and then weigh a Chevy V8. Not only is the Chevy lighter, it has twice the displacement. And, when it’s put in a BMW engine compartment, which it sometimes is in and E92, the compactness of the engine is immediately apparent.

    Old inline 6s had a reputation for low end torque. But it isn’t the inline configuration that’s responsible, it’s the choice of camshaft timing, bore/stroke ratios, relatively restricted breathing with small valves, and other engine design choices.

    Large trucks, class 8, have used both inline 6s and V8s in their diesel engines. Mack and Detroit both made V8s, and no one ever complained about a lack of low end torque. Detroit used to make both an inline 6 and a V8 of the same displacement, and they both had identical torque and horsepower curves.

    I’ve been very happy with my BMW with an inline 6 for quite a few years. No doubt it’s a fine engine, in a fine car, but the fact that it’s an inline engine is irrelevant.

  • avatar
    dividebytube

    I loved the I6 in my old 325i – it was so smooth it was “like butter”.

    My next car, which had an I4 Toyota 2.4L, was a disappointment. Anything above 4k rpm and it felt like a tractor engine.

    The I4 1.6L engines in my pair o’ Minis are actually quite nice – happy revvers. The ’03 with the S/C likes to spin up high to get the power, while the ’09 with the turbo has more bottom end grunt, and seems to fall off in power after 5k. Weird since I would have expected the opposite. But good I4 engines seem to be possible to build.

  • avatar
    FormerFF

    “Furthermore, BMW’s front engine, rear-wheel-drive layout meant it had sufficient engine bay room for a transversely mounted inline six.”

    You sure you didn’t mean longitudinally mounted?

    • 0 avatar
      Featherston

      Yep, I think that’s a typo.

      It’s interesting fodder for discussion, but this article could’ve used a smidgen more research and editing, especially the paragraph about 90 and 60-degree V6s. The author seems to conflate (or at least gloss over the distinction between) rotational and reciprocating forces and firing forces.

    • 0 avatar
      Henry Leung

      Corrected, thanks.

  • avatar
    WheelMcCoy

    Not sure if Ghost Busters can be considered “reborn successfully,” but I get the sentiment. Thanks for an informative article.

  • avatar
    Vulpine

    As I recall, the inline six offered good torque as well, though sacrificed horsepower in the process. Obviously new engines will offer more horsepower for their size, but it’s the torque now that we’re needing in order to let engines run slower while holding a steady speed.

  • avatar
    BigOldChryslers

    > In addition, it’s almost impossible to fit an inline-six into the engine bay of a midsize car. The length of the motor makes it either too wide or too long, depending on its orientation under the hood.

    Isn’t the above still an issue? Mainstream auto manufacturers aren’t going to return to longitudinal engines and RWD for midsize cars, and they won’t want to develop an I6 just to use in limited applications. Consequently, I think that “a similar revival from Japanese and American manufacturers” is some wishful thinking.

    • 0 avatar
      cdotson

      The growing adoption of hybridization and higher-voltage DC power systems allows for full electrically-driven accessories. Eliminating the engine-driven accessories frees up large amounts of room on the end of the engine. Combine this with the trend toward decreasing displacement (smaller diameter pistons) and ever-growing “midsize” cars a transverse I6 is a growing possibility.

      The likely home for an I6 is also going to be CUV/SUVs which could easily have more room for a transverse engine.

      Also using the central PTO would allow for a longitudinal/AWD package. Central PTO could facilitate an I6/I3 multi-displacement mode.

      Lots of reasons to return to I6s.

  • avatar
    theonewhogotaway

    “20 year hiatus in North America.” “after two decades”

    The AMC/Jeep straight 6, in it’s 4.0L iteration, was last used in the 2006 Wrangler. Great engine, had it in an XJ…

    More like 10 years hiatus…

  • avatar
    dal20402

    I don’t think one decision from one manufacturer creates a “comeback.” Volvo ditched its I6, Ford ditched its Australia-only I6, and a few years earlier Toyota ditched its I6. Even BMW is changing the I6 from its volume powerplant to something that’s only for special applications. The packaging downsides of the I6 in passenger cars are just too great to ignore.

    There is so much nonsense in the earlier comments about the supposed power characteristics of I6 engines. The only rule that you can apply based on the number of cylinders is that fewer cylinders at the same displacement is likely to get you more torque. The reason people think I6es are torquey is because most of the I6es they’ve seen are truck engines intended to be torquey, which achieve that goal through other means (high displacement, good breathing down low).

    I6es are used almost universally in the heavy truck industry not because of their torque but because of their smoothness. In heavy trucks, vibration is enough of a problem to threaten trucks structurally. The short-lived Detroit Diesel I4 literally shook trucks and buses to pieces. V6 and V8 heavy truck engines have worked better, but they’ve always been worse on vibration than the I6, which is why the I6 is pretty much all that’s left. (I’m talking about heavy trucks here, not the medium ones where you find things like Power Strokes.)

    • 0 avatar
      JimZ

      “The reason people think I6es are torquey is because most of the I6es they’ve seen are truck engines intended to be torquey, which achieve that goal through other means (high displacement, good breathing down low).”

      the most important “means” is turbocharging. truck diesels have been high-pressure turbo for *decades.*

    • 0 avatar
      TR4

      “The only rule that you can apply based on the number of cylinders is that fewer cylinders at the same displacement is likely to get you more torque.”

      Please cite an example or two.

      I suggest that what really happens is the engine with fewer cylinders has a lower rpm limit and less horsepower.

      For naturally aspirated 2-valve-per-cylinder engines a good rule of thumb is that # ft-lbs = # of cubic inches. No mention of cylinder count.

    • 0 avatar
      Spike_in_Brisbane

      Ford Australia did not ditch the i6; Ford ditched Ford Australia.
      Most decent i6 engines of the past had two overhead cam shafts so no weight saving there.
      I once owned a terrific car with a transverse i6 – the Austin Kimberley.
      Nicest engine I ever owned was in a 1990 BMW 535 (i6)

      • 0 avatar
        RobertRyan

        @Spike_in_Brisbane
        Now trying to make up for their mistake by pouring money into the design and testing operations. Ford’s departure is the domino that started the others to wobble and then fall over

    • 0 avatar
      bhtooefr

      Worth noting that V8 heavy duty engines are still a thing in Europe, largely because length restrictions mean that the packaging of a V8 engine works better in a cabover.

  • avatar

    And when costs or packaging concerns are not an issue, you put two inline sixes together with one block and one crankshaft for the ultimate engine – the V-12.

  • avatar
    red60r

    Also, can’t beat the snarl of an I6. Whether it’s an old Jag, Austin-Healey, or recent Volvo (preferably with Polestar upgrade) the tone is distinctive and just sounds delightful.

  • avatar
    sportyaccordy

    Any engine with a cylinder count that is a multiple of 3 is good with me. I6, V6, flat 6, I’m cool with it. They have the best engine note harmonics IMO. I6s are pretty smooth but I will still gladly take a V6 over a 4 banger any day.

  • avatar
    NoGoYo

    Ford should ditch the 3.5 V6 EcoBoost in trucks and make a beefy 4.5 liter I6 EcoBoost.

  • avatar
    TR4

    The I6 and long-stroke fanboys might benefit from reading this, from when GMC still made real truck gasoline engines:

    http://6066gmcguy.com/478v6.html

    Short stroke, peak torque at 1400rpm from a V6!

  • avatar

    If Aston Martin has any true sense of heritage (except for the token one dictated by the marketing dept.) it asks AMG, with which it works together, to fine tune Mercedes’ 3.0 inline six, and put a compressor on it. Then put it in the smallest Aston, the Vantage ‘V8’. British sports cars, like the E-Type Jaguar, Triumph, Austin Healey, usually featured inline six engines.

  • avatar
    28-Cars-Later

    Straight Eight? Yes we can!

    • 0 avatar
      hachee

      28 Cars Later,
      Do you know if there’s a way to send a private message to someone? I’ve got a question I’d like to ask you regarding those car auction numbers you occasionally post.
      If you see this, please reply, and maybe I’ll figure out a way to send a private message.
      Thanks!

      • 0 avatar
        28-Cars-Later

        No way I know of to ask a private question, ask away.

        • 0 avatar
          Adam Tonge

          Oooooooooo, private. Ssssssssshhhhhhh. 28CL behind closed doors.

          I kid. I kid.

        • 0 avatar
          hachee

          I’m trying to get an idea of what the Manheim value would be on a car. I believe this something that’s not available to the general public. I have a lease return next month, and I’m trying to get an idea of the MMN as compared to my residual value as stated in the lease.

          • 0 avatar
            28-Cars-Later

            Make, model, model year, condition?

          • 0 avatar
            davefromcalgary

            2014 Buick Verano Turbo with Nav, 6 MT, all options.

            80,000 kms, Good well kept condition.

          • 0 avatar
            davefromcalgary

            Im actually serious, btw, the local dealer claims they are wholesaling canadian inventory south. Would love to know what THEY could get something for it, so I could negotiate with them buying the car off me.

          • 0 avatar
            28-Cars-Later

            Dave – Ok, nobody wants that I’m guessing 10K USD or less :)

            I have a 5 o clock I will check after that.

          • 0 avatar
            Adam Tonge

            MY14 Buick Verano Turbo

            11/28/16 Manheim Arena Alberta Regular $-3500 80,000 Above Silver 6G A No

          • 0 avatar
            28-Cars-Later

            @Adam

            You win everything.

          • 0 avatar
            28-Cars-Later

            @dave

            Notice the last one: 4GT 6

            MY14 Buick Verano Premium (shouldbe highest)

            11/22/16 Manheim Georgia Lease $10,500 34,903 Below Black 4GT 6 Yes
            11/09/16 Manheim Dallas Regular $13,900 29,687 Avg White 4GT A Yes
            07/20/16 Manheim Milwaukee Lease $16,500 11,071 Avg Black 4GT A Yes
            06/27/16 Manheim Orlando $13,400 32,785 Avg White 4GT A Yes
            06/15/16 Manheim Milwaukee Lease $16,100 20,890 Avg Black 4GT A Yes
            06/08/16 Manheim Dallas Regular $17,900 4,450 Above Red 4GT 6 Yes

    • 0 avatar
      hachee

      2013 BMW X5 diesel, 30K miles, I’d say very good to excellent condition (a few bumper scratches, no dents, no accidents). Needs two tires.

      • 0 avatar
        28-Cars-Later

        Avg projection for Nov 16 is 26,8
        The MMR projection is 19,7 for Nov 17

        Dealer will ding you a min of $500 for the tires if I had to guess.

        Whats your buyout?

        MY13 BMW X5 (35d)

        11/01/16 Manheim Palm Beach Lease $33,700 14,828 Above White 6D N Yes
        11/17/16 Manheim Darlington Lease $29,000 17,598 Avg Gray 6D A Yes
        11/23/16 Manheim Seattle Lease $31,250 19,693 Above Gray 6DT A Yes
        11/09/16 Manheim Atlanta Lease $28,000 21,347 Avg Gray 6DT A Yes
        11/08/16 Manheim Riverside Lease $29,800 24,504 Avg Gray 6D N Yes
        11/07/16 Manheim Riverside Lease $29,100 27,516 Avg Gray 6D N Yes
        11/09/16 Manheim Atlanta Lease $26,600 27,973 Avg Gray 6DT A Yes
        11/23/16 Manheim Seattle Lease $30,750 28,706 Above Gray 6DT A Yes
        11/22/16 Manheim Nevada Lease $31,500 28,776 Above Black 6DT A Yes
        11/16/16 Manheim Milwaukee Regular $29,000 29,129 Avg Gray 6D A Yes
        11/11/16 Manheim Palm Beach Lease $29,100 29,408 Avg Gray 6D Yes
        11/01/16 Manheim Ohio Lease $28,500 29,651 Avg Black 6DT A Yes
        11/03/16 Manheim Riverside Lease $31,750 29,748 Above White 6DT A Yes
        11/10/16 Manheim Pennsylvania Lease $28,500 29,855 Avg White 6D A Yes
        11/09/16 Manheim Milwaukee Lease $28,700 30,278 Avg Blue 6D N Yes
        11/21/16 Manheim New Jersey Lease $28,000 31,050 Avg Black 6D N Yes
        11/08/16 Manheim Riverside Lease $29,800 31,495 Avg White 6D N Yes
        11/01/16 Manheim Pennsylvania Lease $27,400 32,182 Avg White 6D N Yes
        11/09/16 Manheim Atlanta Lease $28,400 32,400 Avg Gray 6DT A Yes
        11/16/16 Manheim Orlando Lease $27,800 32,990 Avg White 6DT A Yes
        11/02/16 Manheim Milwaukee Lease $26,250 33,740 Avg Black 6DT A Yes
        11/08/16 Manheim Milwaukee Lease $27,300 34,144 Avg Gray 6D N Yes
        11/03/16 Manheim Pennsylvania Lease $26,900 34,459 Avg White 6D Yes
        11/18/16 Manheim Seattle Lease $27,900 35,088 Avg Black 6D N Yes
        11/11/16 Manheim Darlington Lease $26,600 36,010 Avg Black 6D A Yes
        11/11/16 Manheim Nevada Lease $28,200 36,511 Avg Gray 6D Yes
        11/09/16 Manheim Atlanta Lease $28,800 37,633 Avg Blue 6DT A Yes
        11/04/16 Manheim Darlington Lease $27,900 37,678 Avg White 6D N Yes
        11/09/16 Manheim Atlanta Lease $25,400 37,760 Avg Black 6DT A Yes
        11/03/16 Manheim Riverside Lease $30,750 38,488 Above Gray 6DT A Yes
        11/07/16 Manheim San Francisco Bay Lease $28,600 39,094 Avg Black 6D N Yes
        11/21/16 Manheim New Jersey Lease $26,000 39,380 Avg Red 6D N Yes
        11/16/16 Manheim Pennsylvania Lease $26,100 39,460 Avg Black 6D N Yes
        11/17/16 Manheim Riverside Regular $28,000 39,725 Avg Black 6DT A Yes
        11/16/16 Manheim Orlando Lease $25,400 42,887 Avg Gray 6D A Yes
        11/03/16 Manheim Atlanta Lease $24,900 43,486 Avg Black 6D Yes
        11/01/16 Manheim Darlington Lease $24,100 43,746 Avg Gray 6D N Yes
        11/16/16 Manheim Denver Lease $26,250 43,833 Avg Red 6DT A Yes
        11/23/16 Manheim Seattle Lease $23,000 44,607 Below White 6DT A No
        11/15/16 Manheim San Francisco Bay Lease $24,000 45,233 Avg Black 6DT A Yes
        11/18/16 Manheim Darlington Lease $25,900 45,378 Avg Gray 6D N Yes
        11/11/16 Manheim Nevada Lease $26,600 45,866 Avg Gray 6D N Yes
        11/07/16 Manheim New Jersey Regular $26,950 46,037 Avg White 6DT A Yes
        11/02/16 Manheim Palm Beach Regular $26,400 49,252 Avg Black 6DT A Yes
        11/09/16 Manheim New Jersey Regular $23,700 49,669 Below Gray 6DT A Yes
        11/21/16 Manheim Darlington Lease $23,400 50,300 Below Gray 6D A Yes
        11/16/16 Manheim New York Lease $24,400 51,881 Avg White 6DT A Yes
        11/16/16 Manheim San Francisco Bay Regular $25,400 53,640 Avg Gray 6DT A Yes
        11/03/16 Manheim Omaha Regular $24,400 54,711 Avg White 6DT A Yes
        11/09/16 Manheim Atlanta Lease $23,600 54,999 Below Black 6DT A Yes
        11/09/16 Manheim Atlanta Lease $22,200 55,708 Below Black 6DT A Yes
        11/14/16 Manheim New Jersey Lease $23,200 56,931 Below Black 6D N Yes
        11/01/16 Manheim Orlando Regular $23,600 59,916 Below Gray 6DT A Yes
        11/16/16 Manheim California Regular $17,800 80,824 Below Brown 6D A Yes
        11/22/16 Manheim Ny Metro Skyline Regular $18,800 87,393 Below Gray 6D A Yes

        • 0 avatar
          hachee

          Thanks. I am not sure what all that means, but my buyout is about $35K. I think I may be able to renegotiate if the MMR is a good amount less than that.

          • 0 avatar
            28-Cars-Later

            Np. I might bite at 30/31 if I really liked the car, at the very least I would want a free extended warranty at 35 (this being a BMW and all).

        • 0 avatar
          hachee

          I do like the car, and I’m thinking along the same lines. Definitely need extended warranty, but I’m quite sure this isn’t worth 35 plus warranty/CPO cost. Thanks again.

          • 0 avatar
            28-Cars-Later

            I’d say you’re playing with 4-5K in margin. BMW corporate would probably rather sell you a new one and keep you on the leasing treadmill rather than offload, so why don’t you see what they want to do for you. Otherwise the lease agency gets to eat the margin on the block or issues the cost of CPO if they think they can retail it (hint: I bet they can’t, few are buying diesels post VWgate).

        • 0 avatar
          OldManPants

          Jesus H… 28CL makes tracking used cars a science.

          Look at the colors listed; it’s another Dismal Science.

  • avatar

    As the owner of a BMW 330ci and a Toyota FJ62: I agree!

  • avatar
    Kyree S. Williams

    Volvo had transverse-mounted I6 engines in most of its cars (the largest of which displaced 3.2 liters) until very recently. I think it was through 2014. I beleiebe they were Ford group engines as well.

    • 0 avatar
      CoreyDL

      i no car what u beleiebe!

    • 0 avatar
      Marko

      It looks like you could still get the twin-turbo I6 on the 2016 S60 T6 AWD. This engine (“SI6”) was developed during the Ford era, though it was an evolution of the Modular (“white block”) engine, which then-independent Volvo originally developed in the 1980s. Porsche may have had some input, though it is unclear to me how much. It was not related to the Australian Ford design discussed earlier.

      https://en.wikipedia.org/wiki/Volvo_SI6_engine

      https://en.wikipedia.org/wiki/Volvo_Modular_engine

    • 0 avatar
      red60r

      Note that the Volvo 3.2 liter I6 is the un-supercharged version. Displacement drops ~300cc for the turbo versions, with the difference expressed in thicker cylinder walls.

  • avatar
    CoreyDL

    “In addition, it’s almost impossible to fit an inline-six into the engine bay of a midsize car. The length of the motor makes it either too wide or too long, depending on its orientation under the hood.”

    The Toyota 3.0 I6 begs to differ.

  • avatar
    narcoossee

    Is it me, or does this article seem dangerously close to this one, over at R&T? http://www.roadandtrack.com/new-cars/videos/a8645/the-enginerdy-dept-straight-six-revival/

  • avatar
    namstrap

    I was very lucky to have had a 1979 CBX. That was the first year, and it made 105 HP. They had to reduce it the following year to 100 to get it into Germany. There was some kind of law limiting motorcyle horsepower. It was really smooth, but way too complex. Six carburetors to balance, and 24 valves adjusted by shims.
    Did you people in the States ever get the Chevrolet Epica? The sister car was the Suzuki Verona. It was a Daewoo product, their biggest, and it had an in-line six engine sideways displacing 2500 cc. That was the last east-west in-line six I can remember. They only sold the car here in Canada for a couple of years.

  • avatar
    theoldguard

    After my ’87 325is, all other car engines, especially the inline-4’s, seemed like agricultural implements. Honda does them a little better, so they are John Deere. So often people who rode in that BMW said, “it’s so smooth.” Many other cars I had made more power all over the rpm scale, but it is that BMW inline-6 that holds my fondness above all others. All this love despite the fact that it snapped its timing belt right after the warranty expired, I think it was 65K. It was only then that I learned what an “interference” engine was. I regard this car as the beauty queen that snapped and went psycho. Would I do it again? Of course. Bring back the inline-6.

  • avatar
    toneron2

    Oooh – sorry Charlie. The Best Six is the Boxer 6. Research it.

  • avatar
    Jeff S

    I disagree about the last Colorado with the 3.7 I-5 being a slug. The engine itself has good acceleration it is the 4 speed automatic in it that downshifts when you accelerate too fast. I have a 2008 Isuzu I-370 crew cab with the I-5 3.7 and that has been my experience over the last 8 years of ownership. The I-5 is a great engine it just doesn’t have the cache of a V-8 or a turbo V-6. It is a very good engine with a steel timing chain and not as complex as some of the V-6s. Just because an engine is not popular doesn’t mean it is no good.

  • avatar
    don1967

    My Volvo 3.2 I6 has a nice smooth snarl to it. It hustles 4,000 pounds of steel along at a decent pace, while asking for little more than 87-octane fuel and a fresh crankcase of 5w30 conventional oil every 12 months. Try that with your turbo-four.

    The story of why they chose the transverse-I6 layout is about cost + safety. It’s a mechanically-simple engine with lots of empty crush space fore and aft of the block.

  • avatar
    DJEmir

    Star Wars was not a reboot, remake or redo though it was a continuation whereas the others were remakes. So not quite the same. They didn’t have to completely redo Star Wars, they were pioneers and were partly responsible for furthering the Special effects technology and were ahead of their time enough that it still plays well with or without the digital touches added in later.


Back to TopLeave a Reply

You must be logged in to post a comment.

Recent Comments

  • ToddAtlasF1: Because they know EVs belong back in the Victorian era, where they were first rendered obsolete by the...
  • FreedMike: This is definitely not good news. China is probably critical to the company’s health.
  • Fordson: Some makes just should never produce SUVs…this is one of them. Look at the Maserati car in the group...
  • FreedMike: Toyota. Why do you think they haven’t invested in EVs?
  • redapple: Who will buy Tesla? GGM?

New Car Research

Get a Free Dealer Quote

Staff

  • Contributors

  • Timothy Cain, Canada
  • Matthew Guy, Canada
  • Ronnie Schreiber, United States
  • Bozi Tatarevic, United States
  • Chris Tonn, United States
  • Corey Lewis, United States
  • Mark Baruth, United States
  • Moderators

  • Adam Tonge, United States
  • Corey Lewis, United States