Return Of The Straight Six

Some things in life are just right. Ketchup on fries. A nice cold beer on a hot summer’s day. A straight six engine in a sports car, or any car for that matter.

In my mind there’s nothing more right than lining up six cylinders on a common block, and for decades upon decades this was the way many manufacturers loved to build their engines. But then impact regulations forced them to look at other options; inline sixes are are physically long and thus there were issues around cabin penetration during a front-on collision.

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For most manufacturers looking for a mid-sized engine, V6s seemed like an easier and cheaper solution to get around the problem. They are much shorter, can be mounted longitudinally or transversely, and are able to power rear-wheel drive, front-wheel drive, and all-wheel drive vehicles of every type. But now that’s about to change, or at least it is for Mercedes-Benz, and possibly more manufacturers in the near future.

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This to me is exciting stuff; Mercedes-Benz is an automaker that built its success and brand on the back of inline six motors. There were dropped in favor of V6s that made financial sense at the time, but now Mercedes has come full circle, and it’s largely thanks to BMW – who never strayed from the straight six formula – that this is happening.

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You see, while cunning engineering allowed BMW to figure out how to make straight sixes part of the collapsable structure in case of an impact, it’s the modular layout that they are built around that has caught the attention of Mercedes-Benz and other manufacturers. By adopting a modular 500cc cylinder design, BMW is able to share bottom end and cylinder head components across the board, from their three and four cylinder engines, over to their core – the straight six – and onto V8s and V12s.

An inline six is naturally balanced, meaning there is no need for complex balancing shafts. It also frees up far more space to allow for packaging and ancillary placement, not to mention thermal management which gives a cold intake side where you can arrange more heat-sensitive components.

Mercedes-Benz Sechszylinder-Benzinmotor M256

Throw every last bit of new tech you could think of at it, like direct injection, variable valve timing, twin-scroll turbochargers, electric superchargers, and hybrid systems, and it all arranges itself beautifully around this inline design. I’ve just pretty much described Mercedes-Benz’s latest motor, a force-fed, 3.0L straight six with a 48V hybrid fill system built into the flywheel/starter-generator assembly.

Mercedes-Benz Sechszylinder-Benzinmotor M256

The engine is offered into two guises, one powering the upcoming CLS450 which develops 362hp and 369lb-ft, and a more powerful variant equipping the AMG53 version which delivers 429hp and 384lb-ft. The Mercedes-AMG version is the one that features a little electric supercharger to fill the gap at lower RPM, taking full advantage of the 48V system which helps eliminate power-sapping belt-driven ancillaries like A/C compressors and alternators.

This is the type of evolution of the straight six that I personally always hoped manufacturers like Nissan and Toyota would do. How amazing would it be to see Nissan take the RB26’s winning formula and create a new generation take on it? Toyota could do the same with the 2JZ. But both automakers continue to rely on the V6 formula, either with forced induction or mated to a hybrid/electrified drivetrain. Next to BMW and now Mercedes-Benz, it makes it look like they are a good generation behind where we should be going.

To give you an example, the AMG version of this straight six is right behind the company’s 4.0L twin-turbo V8 in terms of performance (in its more entry-level configuration) with the six cylinder using 20% less fuel and emitting 20% lower CO2 emissions. The engine runs so smoothly and efficiently that the idle speed was able to be lowered from 610rpm to 520rpm.

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Jaguar Land Rover seems to be the next manufacturer that may follow suit. It plans to stop buying bigger engines from Ford by 2020 in favor of developing larger versions of its modular Ingenium 500cc cylinder motors, the straight-six being the most obvious progression to its current four-banger. With Aston Martin now using Mercedes engines, maybe we’ll even see a 450-500hp entry-level Vantage…

The fact that this is becoming a thing makes me happy; we now have something cool to look forward to before everything out there really starts going electric. I’d love to hear your take on this topic, so let’s continue the discussion below. Straight sixes forever!

Dino Dalle Carbonare
Instagram: speedhunters_dino
dino@speedhunters.com

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1

Well, while reading your first lines talking about dropping the L-6 for V-6 i was only thinking of BMW, thank you guys for holding the torch for this long. This new engine of MB seems promising and hope the Japanese buddies join the party soon (with their own engine not shared with BMW or others).

As a personal opinion, i still can't see the full electric coming soon and this new engine is a proof,it's an inter-phase but i think it would be longer than stated by manufacturers since it's pleasing everybody.

Author2
Dino Dalle Carbonare

I don't think the Japanese will, unfortunately. Look at the new Supra with BMW powertrain. Nissan uses a Mercedes 4-cylinder in the Skyline in Japan, so maybe they could extend the agreement to used these new ones, one for the next Z one for the Skyline! Now that would be rather nice. Full electric is another 10 years away at least

3

Dino, you own a 6 cylinder 4 series (if I remember correctly, you hardly update the project drop top) and RB26 GTR34, do you think their engines are more enjoyable than their v6 equivalent? Like R34 vs Z34 or something equivalent to the 4 series? Basically, does engine configuration plays a significant part in driving performance or enjoyability? Thanks

Author4
Dino Dalle Carbonare

Yeah must update Project Drop Top too!! Haha. Honestly yes, I like the smoothness of a straight six, plus the sound which a V6 could never, every match. I like the Z34 but I've never liked the VQ family of engines. They're lazy, rough and uninspiring at higher rpm. Sure you can make them better, like Tanabe-san did with his Z33 back in the day at Amuse, but I just wish they just drop the whole V6 thing. Nissan has a massive history with straight sixes, from the S20 to the L-series to the RB.

5

Hi Dino

Sorry for the late reply, I have been busy recently. Yeah I'm curious at how does the inline 6 of the BMW compares with the legendary samples like the RB, maybe you can include that on the next update of the project drop top? I see, so it's more of character difference between the two configuration rather than performance. Yup, brand like Amuse surely made the Z family special, I still remember gran turismo having the Amuse Nismo 380RS Superleggera in the game. Sure would love to see Nissan do modern incarnation of the RB, maybe to go head to head with the new supra.

6

Yes! This is some great news! Thank you for sharing this!

7

Straight Six? YES PLEASE!
(Never forget the lovely music from the S20 and L-Series...)

Author8
Dino Dalle Carbonare

They just can't be matched for sound. Well maybe a V12, but then again that's 2 straight sixes on a common crank lol

9

Agreed, my old man had an E34 with a 2.5L straight six from new in 1991, loved the sound of that motor. 525is, factory M5 body kit and sports suspension, exhaust and a limited slip diff back when such things were an option you could tick on the purchase list (imagine that, using a pen and everything!). Wish I could remember the reg, would love to know if it's still about.

10

very exciting. some engine configurations are just better than others. the V8 and I6 occupy the top spots in my mind. glad to see I6's making a comeback.

11

What about the old Ford slant 6? Another great straight six that allows for a lower hoodline.

12

Yes I did, my bad.

13

I think you mean the Chrysler slant six, the Ford one was upright. And built until 2016.

There is a new GM diesel inline six coming for the big pickups too which I was surprised to see.

Jaguar and Aston Martin with inline sixes again sounds good.

Author14
Dino Dalle Carbonare

Ford has to be the Barra. 4L cast iron block and the potential for stupid power.

15

Yes, I have driven tens of thousands of miles in a few Barras, mostly non-turbo though.

The most powerful one I rode in ran 9s, made about 700 who but on the highway felt like any other car, smooth and quiet.

I read recently that they looked at replacing the cast iron block with magnesium because it is mined here, but that would have been during the time when Dearborn was slowly killing the Falcon so an investment like that was never going to happen.

16

Dude, an I-6 Hybrid Z-car! <3 <3 <3

17

And a New-jay-zee!

18

And an american slant-6!

19

As much as I enjoy straight sixes, particularly the noise. I'm not on the bandwagon that inline sixes are overall better than their V counterparts. The V engine just offers a much more compact and easier to package engine layout IMO, while also being significantly shorter and allowing a better weight balance. If youre to consider the engines and not think about putting them into a car the straight six is very appealing, but when considerations such as wheelbase, weight balance, interior room, and even polar moment of inertia, the straight engine just compromises a lot of the cars design.

20

You could easily build a better I6 chassis to address the shortcomings you have listed. Like Porsche, you could develop a rear transaxle, that would allow you to obtain a true 50:50 weight balance. The increase in polar moment is obvious, but that actually could make it a better car for drifting, since, like a heavy flywheel, it balances out what might otherwise be a twitchy rear end.

21

Compact and easier to package? Perhaps in Naturally Aspirated form... Turbocharging a straight six it a much better affair than a V engine.
Even from factory. Nissan Z32 (300zx Fairlady) says Hi. Lol

22

Its the symmetry of the design. I6s are inherentlu balance and don't require extra things to offset vibrations. So smoother and more efficient.

23

as with anything there will always be design trade-offs. If you are talking about FR type cars which are meant to sit 4 adults, then yes the shorter V packaging will help with all of the things you have mentioned. Those design considerations change when you are working on a 2 seater FR or MR car as packaging and weight distribution can be shifted around due to a smaller cabin area. In the end it depends on the design parameters of said vehicle which will determine how much an in-line 6 will compromise it. That being said, BMW has made excellent handling cars with straight 6"s for quite some time with very little compromise in their design goals.

24

It might be a straight-six, but with factory forced induction and electric assist it won't be the same anymore.

Author25
Dino Dalle Carbonare

I'm just happy it's happening. Keen to try it out, but I can't even imagine what a massive PITA it would be to tune it!

26

ICE's seem to be having their last hurrah right now with some cool technologies being developed.

27

It's even got plenty of headroom on the design. This I6 could actually benefit from having a linear electric generator integrated with the engine. That would truly be revolutionary technology. It's not even that difficult to develop, but I'm sure there are some serious packaging issues.

Author28
Dino Dalle Carbonare

Indeed!

29

I hope my RB will be able to sing again this summer, just so much left to do! New crank and all

Author30
Dino Dalle Carbonare

Same here. And all I need to do is fit cams. Wish Do-Luck weren't so busy!

31

Neat! What did you end up with? High lift and fully rebuilt head?

Would like to try every camshaft out there to see how they affect the engine sound..
So you should atleast include a before/after soundclip :)

Author32
Dino Dalle Carbonare

Just a simple cam upgrade for now, as well as a metal head gasket

33

I for one am very pumped! I've been around straight 6's ever since I was into vehicles; jeep 4 liter, various Cummins, and even (arguably) the VW VR6. The sound alone, and torque for days, they r just so great! Go Benz! Do it Jag! New jay zee! I want em all!!

34

Yes! Straight sixes forever!

Love this article Dino. Exciting news.

I've always held credit to BMW for sticking with the straight 6. The ongoing development is something Toyota and Nissan missed out on. When I heard the new Supra was getting a BMW engine, I was relieved. I don't think Toyota could match the RnD, 'overnight' so to speak, that they've missed out on.
In my eyes, there was no better candidate than BMW for the straight six that the new Supra both deserves and needs :)

Author35
Dino Dalle Carbonare

It was all about cost. They obviously don't plan to use the engine in any other Toyota models, so spending a billion $ to develop a motor for a niche product is not what the bean counters would ever sign off. I think if Toyota did develop a 3JZ (?) it would come up with some crazy advanced tech for sure....

36

Yeah that's true. The JZ and RB engines were used in multiple cars in their line-up. But Nissan and Toyota don't want to be cool anymore lol.

37

I own a 2005 330ci with a badass straight six and I'm glad to see that other manufacturers are following the formula that never gets old.

38

Hej Dino, are you paid by dealers/oem's to promote this?
All this 'new technology' does is add unneccessary complexity and weight without actually increasing the thermal efficiency of the motor to a substantial degree. All the while consuming more resources in maintenance, creation and disposal, but with maybe a bit more mpg and over-reliance on the oem's for repairs.
On top of this does the driving experience offer any more enjoyment than what was provided to us in the golden age of 90's Japanese turbo beasts? I mean we are still developing and maintaining these dinosaurs with as much passion as when they first came to be. Now we are offered these over priced, over complex alternatives that try hard to capture our imagination. Good luck maintaining the hybrid systems and other electric paraphernalia in 30 years time, the old K series and 4G63 will still be hammering down the road on nitrous in 60 years time I bet.
I know you won't trade that ancient rb26. It's a Mad Max world and we are awaited on the fury road. Keeping alive the traditional spirit of boosted internal combustion on the highways and backroads througout the world...

39

The manufacturers have minimal say in any of this, their hands are being forced by uneducated governments who have no real understanding of whats going on. All the manufacturers can do now is to keep finding lots of little ways to make gains in the hope that they all add up to a big one.

Some big ICE tech is coming soon though, such as active variable cylinder deactivation, variable compression ratios and on demand variable compression and spark ignition. They'll make big differences and hopefully take away some of the reliance on "auxiliary" tech to keep emissions and consumption down.

40

Mercedes are producing over 50% efficiency in their F1 engines. Of course, they use much different turbocharging technology, but they are most certainly using that knowledge to improve their production engines.

41

Amen! Natural balance forever.

42

I don't know but the term 'sports car' has gone blur. A Jaguar with their V8 or an Aston with their lazy V12 can be considered a sports car too. I'd say yes to cars that traditionally have in-line 6, but no to Mercedes. They should have big V8.

43

The greatest attribute of the single-turbo DOHC straight-six is its clean, simple elegance.

One cylinder bank, one cam for the intake valves and one for the exhaust side, one exhaust manifold, one turbocharger feeding one intercooler, going into one intake tract, flowing into one exhaust pipe.

Seeing a theme here?

To say nothing of being inherently balanced, having a one-to-one alternating arrangement of main and rod bearings to make it supremely tough and having all the plugs in a straight line on top where you can get at them.

There's just so much about the design that makes sense.

And no other engine has this combination of positive characteristics.

NA V8s have inherent structural weaknesses due to their One Main-Two Rod-One Main bearing layout, I-4s are all top end, V6s need all kinds of weird geometry to function mechanically, turbo V-configuration engines are gigantic and need complicated plumbing, etc.

And not a single one of them is inherently balanced.

In fact, the only real drawback is length.

44

If reliability problems that have plagued BMWs turbo'd IL6s like the N54 (seals going out, turbos getting worn out quickly, and cheap components like the plasitc electric water pump) could be fixed before production of these new motors that would be AMAZING! im all for forced induction IL6s. N54s are some of the more underestimated engines ever!

45

All of those issues you mentioned aren't even specific to the IL6 configuration anyway haha.

46

I knew BMW and Ford were making straight sixes that seemed pretty interesting with BMW's engine being stupid amazing and Ford's Berra straight six thing from down under still kind of lagging behind, but what i hope is that they could be bought as a crate engine and see what people can do to them and if they out preform RB's and JZ's that have been built up and tinkered with for so long.

47

The straight-(insert number 3 or larger) paired to a strong and notchy manual transmission is as elegant and emotional as ICE gets. As an enthusiast, the electric drivetrain (atm King Tesla is still figuring this out) is the most elegant drivetrain possible... but if you dont know how to program your E car to perform, then makes sense you feel butthurt when an autonomous electric inevitably destroys your human pride at being “fast”. Enter the romance and validity of ICE: Its our history - and it’s the difference between archery and ICBM’s. Real racing and serious mobility will evolve to favor the iPad on wheels, but when you just wanna DRIVE...

Youll see nothing but inlines and manuals for miles.

48

ICE?
As in... in-car entertainment? lol
Or...?

Completely lost me with "Enter the romance and validity of ICE: Its our history - and it’s the difference between archery and ICBM’s"

49

Internal combustion Engine :)

50

If there's no alternator, what recharges the 48V power supply?

51

The integrated starter generator where the flywheel would normally be. They can charge normally like a traditional alternator, can regen on braking and provide electric assist and torque fill during acceleration. They're a clever bit of kit that we are all going to have to get used to, within 5 years most new cars will have one.

52

Sorry but I don't think straight 6's sound that good. Compare an M4 to a F-type V6. One of them makes all sorts of lovely noises at different frequencies and different throttle loads, and the other makes the same bland noise, varying in volume depending on revs. A good aftermarket exhaust opens up the M4's noise a bit but it's still not exactly inspiring. In fact it's so uninspiring they have to pipe noises into the cabin to trick you into thinking it sounds good. I know the M4 is turbocharged and has some of it's noise muffled, but there's plenty of V6 turbo engines that still make all sorts of majestic noises.

53

The fact Mercedes using R6 again has nothing to do with BMW, but with technical advantages like you also mentioned. You are a little bit late to this topic, Mercedes said already many years ago the R6 will be back, its not like someone forgot it and then suddenly they discovered that BMW still uses R6. Please get your facts right.

And it wont all go electric, when do you guys will start to realize it? Electric cars are from the past. Too expensive, too much disadvantages thats why nobody wants them, but the most important thing is that there arent even enough resources to build these cars for everyone. So you will see Diesel even in 30 years, because its the best technique out there. And look up for the synthetic fuel topic. When this is going to be produce in masses, no one will buy a crap electric car. Thats the true future and its even clean for the enviroment and cars sound right, not like an haircutting machine.

Nice topic though.

54

"Return of the price tag."

55

Les than two weeks ago we sold out old BMW with M54 in it. Now we drive also a Beemer but with N20 in it. There is over a decade in age between the cars and engines, and in spite of all its technological gimmicks the new in-line 4 turbos just don't match the creamy smoothness and sound of in-line 6. Sadly they don't make them as they used to, but then again it's for the better. It's hard to argue with the benefits of newer tech, although, newer is not always better. One thing that puzzles me is the focus on ICE by MB. Isn't everyone moving more toward hybrid-electric drives? With their stellar F1 record in the last few years, especially with the return of compact V-6 turbos, one would expect more of that tech.

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