Return of the inline-six: Why the classic engine layout is making a comeback

[kscarbel2]

Richard Truett, Automotive News  /  October 24, 2017

Nearly 70 years since it was blown away by the high-compression Oldsmobile Rocket V8, the inline-six engine is poised to make a comeback.

I'm not the first to connect these dots, but the reason for the return of the inline-six has everything to do with manufacturing efficiency and not because of an inherent fault of the V-6. As V-8s fade away, the V-6s they spawned will also diminish in numbers.

BMW, which never abandoned the inline-six, has created the template for the modern modular inline engine family that other automakers are adopting. At BMW, each cylinder is 500cc and the engines are modular, meaning that they use the same basic menu of internal parts, such as valves, pistons, bearings and pumps.

"The advent of the modular 500cc cylinder has brought us a flurry of 2.0-liter I-4 engines, 3.0-liter V-6 engines and 4.0-liter V-8s. A lot of this was due to cost," says AutoPacific analyst Dave Sullivan. "Being able to use the same hardware in multiple applications helps to bring costs down. The inline-six is naturally harmonically balanced, reducing the need for balancers or any expensive treatment systems," he added.

When Jaguar Land Rover developed its acclaimed Ingenium gasoline and diesel engine family, it used BMW's 500cc per-cylinder and modular component strategy, but with engineering twists of its own. JLR's announcement last month that it plans to stop buying gasoline engines from Ford's Welsh engine plant in 2020, opens the door to larger Ingenium engines. JLR officials won't confirm six-cylinder Ingeniums are on the way, but it is a sure bet they are.

JLR buys its V-8 and V-6 engines from Ford, and without those engines, it would have only turbo four and hybrid vehicles -- which would not develop enough torque to provide the kind of performance a Range Rover needs to take on Bentley and others. But a supercharged 3.0-liter Ingenium six could easily replace the 5.0-liter V-8.

JLR's plan to halt the Ford V-6 and V-8 gasoline engine purchases in 2020 indicates the six-cylinder Ingenium engine will likely be ready for the 2021 model year -- or sooner if JLR discontinues the V-6 before the V-8.

As three- and four-cylinder engines continue to deliver more power and efficiency, it's far less expensive and disruptive to add another pair of cylinders for a bigger engine with more torque than to build a V-6 that doesn't share its parts with a V-8.

Mercedes' new inline-six, a 3.0-liter, comes in two flavors, Automotive News affiliate Autoweek reports, including one that cranks out 435 hp.

But there are problems related to inline-sixes. Most are longer than the V-6s they will replace, making it tough to mount the engine in front-wheel-drive cars because the engine's length leaves little room for the transmission. That length also can be problematic for rear-wheel-drive cars, which may need longer hoods to accommodate the engine.

And then there's safety.

Engineers appear close to solving a few lingering safety problems that they didn't have to deal with when a V-6 was installed. "One of the long-standing issues [for the inline-six] has involved the length of the engine and crash standards. It appears that manufacturers are confident they can have an engine 'deform' and not penetrate the cabin," says Sullivan.

But, if you've driven a BMW six lately, you know how smooth and silky an inline-six can be. Now, with direct injection, variable valve timing, electric superchargers and electrification, the inline-six just may be the configuration that propels the internal combustion engine to the finish line.

.

[HeavyGunner]

Jeep ran with the 4.2l (carbureted) then the 4.0l (fuel injected) for years. Until the JK I believe and it’s a fantastic engine. Lasts forever, has good power and isn’t real heavy. The only down fall I’ve seen in most of these six cylinders (v or in-line style) is the fuel mileage is rarely any better then a modern v8 so I usually opt for more power for towing and hauling since the mileage is usually neglibly different when empty. 

Edited October 25, 2017 by HeavyGunner

[Hobert62]

I know of a few 4.0 jeeps in the area with 300,000 miles on them and still going.   I always wondered why ford & chevy went with a v8 diesel rather than a inline version.   

[HeavyGunner]

2 hours ago, Hobert62 said:

  I always wondered why ford & chevy went with a v8 diesel rather than a inline version.   

Me too. 

[Red Horse]

3 hours ago, HeavyGunner said:

Me too. 

 

5 hours ago, Hobert62 said:

I know of a few 4.0 jeeps in the area with 300,000 miles on them and still going.   I always wondered why ford & chevy went with a v8 diesel rather than a inline version.   

well with Detroit Diesel coming out with all these smaller inline engines, and Isuzu and Hino doing well in the lower classes, perhaps Ford and GM might just get the idea.  Not every class 5,6 and 7 truck needs a 350+ HP torque monster IMO

[57 bcr]

Always  been a 6 banger fan myself. Starting  with  my first  a '67 F-100,then a '66 (both  with  240's in them). Reminded me of  the big truck  sixes. Easy to work  on and ran forever. Ford lost my interest  when they discontinued  the 300. Have a '97 Wrangler 4L with  186,000 that  to this day, does not use any oil (although  the frame is about  to rust in half!). I applaud  the return  of the in-line 6. Al  

[j_martell]

Always loved the I6.  Had a 4.2L Jeep back in the day, and knew lots of guys with the 4.0L. Solid, powerful, reliable, smooth....and the sound.  Old friend had a 91 F-150 with the 300CI I6, that thing wouldn’t die.  Had nearly 700,000km on clock when he was done with it.

[VaPatentman]

I too had 300 six that wouldn't die

[Jamaican Bulldog]

Inline sixes and V12 engines are often considered the most balanced configuration for engines to deliver smooth power. That is one reason why BMW kept inline sixes when others went to V designs. One of the reasons V designs for 6s replaced many of their inline predecessors  was because the V design allowed the engines to fit in more compact spaces. This  especially as many car and SUV platforms shifted from longitudinal  powertrain configuration ( engine mounted north to south with rear wheels as main driving wheels) to transverse set ups ( engine mounted east/west or vice versa or front wheel drive based).

The inlines are definitely easier to work on especially with so many accessories mounted on engines nowadays.

 

[Ezrider]

inline sixes are a great design, smooth reliable, well balanced. make good torque i think they mostly fell out of favor due to packaging. i wouldn't mind seeing more inline 6's on the market. 

[gxbxc]

yea don't forget the Hudson straight 8 and the Buick straight 8, the Hudson Hornet ruled NASCAR for years. It was kinda fun watching some old grandmother put her Hudson in a parking space ,kinda like watching her park an old needle nose KW.

Edited October 26, 2017 by gxbxc

[Dirtymilkman]

Gm had the Atlas series engines for years. A 4, 5 and 6 cylinder with interchangeable parts. The 5 banger had like 250+ hp and the 6 was 300 with lots of torque. Had one in a trailblazer and loved it. 

[Hobert62]

8 hours ago, Dirtymilkman said:

Gm had the Atlas series engines for years. A 4, 5 and 6 cylinder with interchangeable parts. The 5 banger had like 250+ hp and the 6 was 300 with lots of torque. Had one in a trailblazer and loved it. 

My patents had a trailblazer and yes it ran pretty good.   The tranny seamed pretty lame for the motor though.  

[blackdog2]

When something is good and dose not die WY would they keep building it like a DM-600                    

[Keith Pommerening]

9 hours ago, gxbxc said:

yea don't forget the Hudson straight 8 and the Buick straight 8, the Hudson Hornet ruled NASCAR for years. It was kinda fun watching some old grandmother put her Hudson in a parking space ,kinda like watching her park an old needle nose KW.

The Hudsons that ruled NASCAR, when stock cars were STOCK cars, ran a 308ci inline six flathead.  It would turn 6000 rpm back then with the 7X engine.  Their handling might have been the biggest factor.  Talked to a old guy who use to run Olsmobiles at Minnesota State Fairgrounds.  He told me he would blow by the Hudson in the straight and while his Olds was jumping and hopping in the corners the Hudson would motor around him like he was on a Sunday drive!  Also said the winner was usually the one that didn't brake-down.  

Hudson was the first to produce unibody cars with a front clip like Camaros, Novas, Mustangs...  The front steering arms connected in the center of frame and were actuated with a bellcrank.  No drag links.  Another inovation I've seen on no other cars is the rear sping layout.  They angled the rear spings toward the center of the front axle, in a truncated "V" pattern.  Wider in the rear and narrower in the front.  Like running a line from the front axle steering pins, through the steering ball joint and back to the center of rear axle.  The Ackerman principle drawn out.  Don't know if that was a big deal, but interesting concept.  They were also overbuilt because no one knew what would fail first with the unibody/front clip build style.

[kscarbel2]

"The advent of the modular 500cc cylinder has brought us a flurry of 2.0-liter I-4 engines, 3.0-liter V-6 engines and 4.0-liter V-8s. A lot of this was due to cost," says AutoPacific analyst Dave Sullivan. "Being able to use the same hardware in multiple applications helps to bring costs down. The inline-six is naturally harmonically balanced, reducing the need for balancers or any expensive treatment systems," he added.

-----------------------------------------------------------------------------------------------------------

Relating to that statement in the above article:

Why 0.5-Liter Cylinders Will Soon Dominate Automotive-Engine Design

Don Sherman, Car & Driver  /  January 27, 2015

A decade or so ago, a team of German university scientists settled on 500 cubic centimeters as the ideal per-cylinder displacement for internal-combustion engines. A 500-cc cylinder with a stroke length larger than its bore diameter, these forgotten pioneers concluded, benefits the combustion process by minimizing the engine’s internal surface-to-volume ratio as the piston nears top dead center. Seeking to optimize power and fuel efficiency while reducing emissions, the three local powerhouses—BMW Group, Mercedes-Benz, and Volks­wagen Group—promptly joined the 500 club with boosted, direct-injected, long-stroke engines. Fiat Chrysler, Jaguar Land Rover, and Volvo are also applying for membership. Additional brands will surely follow, in part because 500-cc-displacement intervals align nicely with existing global taxation statutes. While hybrids and electrics will assist the move to better mileage with lower emissions, updated versions of Nikolaus Otto’s 139-year-old engine—many with 500-cc cylinders—will continue to do the heavy lifting.

Thus far, BMW is the most enthusiastic proponent of the 500-cc cylinder, with half-liter-based three-, four-, and six-pot gas and diesel engines either in production or about to be introduced. BMW’s newest family of TwinPower Turbo gas engines, which launched in the 2015 Mini Cooper Hardtop, shares its 82-mm (3.23-inch) bore and 94.6-mm (3.72-inch) stroke dimensions, plus direct fuel injection, variable intake- and exhaust-valve timing, and variable intake-valve lift systems. This modular approach enables 60-percent commonality of the component parts across three gas engines and 30 to 40 percent with the corresponding two diesel engines.

It’s not just the 500-cc displacement that matters, but also the dimensions that yield such volume. While a cylinder with a smaller bore than stroke (a so-called under-square design) contradicts the classic approach to maximum power at stratospheric rpm [see “Different Strokes”], there are compelling reasons for this move. A small bore shortens the flame travel needed to consume the fuel-air mix and diminishes quenching of the flame at the bore’s periphery. With smaller piston crowns and a more compact combustion chamber, there’s less heat lost to the cooling system. Smaller bores trade shorter overall block length for a modest increase in height, handy for jamming potent engines into tight confines.

One hardship enthusiasts must bear is slightly lower redlines. In exchange, we get better mileage (when we can resist the urge to pin the throttle) and enhanced flexibility attributable to the broader spread between torque and power peaks. Considering the global statutes in place mandating higher efficiency, we’re happy that Otto’s engine has more life left in it.

Different Strokes

Here’s a look at two different approaches to making power. Mercedes-Benz’s 6.2-liter AMG V-8 is the last gasp of the old way, but it’s unlikely to survive until 2025. Its replacement is the twin-turbo 4.0-liter new-wave V-8 spreading throughout AMG’s lineup.

Herewith, 20 boosted engines built around small-bore, long-stroke 500-cc cylinders:

BMW GROUP 1.5-liter inline-three 2.0-liter inline-four 2.0-liter diesel inline-four 3.0-liter inline-six 3.0-liter diesel inline-six FIAT CHRYSLER 3.0-liter diesel V-6 JAGUAR LAND ROVER 2.0-liter diesel inline-four 3.0-liter V-6

MERCEDES-BENZ 2.0-liter inline-four 3.0-liter diesel V-6 4.0-liter V-8 VOLKSWAGEN GROUP 2.0-liter inline-four 2.0-liter diesel inline-four 3.0-liter V-6 3.0-liter diesel V-6 4.0-liter V-8 6.0-liter W-12 VOLVO 2.0-liter inline-four 2.5-liter inline-five 3.0-liter inline-six

[kscarbel2]

20 hours ago, Hobert62 said:

I know of a few 4.0 jeeps in the area with 300,000 miles on them and still going.   I always wondered why ford & chevy went with a v8 diesel rather than a inline version.   

Ford and GM went with V8 diesel designs, in the North American market, because Americans like V8s. Dodge couldn't afford to design their own and the Cummins 5.9-liter B Series was available off-the-shelf. 

The Cummins of course was a significantly better engine.

Isuzu (6.6L Duramax) doesn't even sell a V8 in the global market (Years ago, like all the Japanese heavy truck brands, they built many V8s....Euro 1 and Euro 2).

Ford told Austrian contract design firm AVL to create the current PowerStroke as a V8, feeling a V8 would sell better.

[57 bcr]

21 hours ago, Dirtymilkman said:

Gm had the Atlas series engines for years. A 4, 5 and 6 cylinder with interchangeable parts. The 5 banger had like 250+ hp and the 6 was 300 with lots of torque. Had one in a trailblazer and loved it. Al  

Have an '03 Envoy (and had an '03 Trailblazer) with  the 4.2L six  ,that the wife and  daughters  can't  destroy. That says a lot at my address! Well  over 200,000 on both  with no engine  problems. The abuse  both me and the Envoy take, it's  a wonder we're still here! Al  

[Timmyb]

Ford Australia stuck with their straight 6 for 46 years. It was always an exception performer. 

In its last incarnation it became turbo charged and ended up with 335kw (450hp roughly) and has the low down torque you'd normally associate with old school v8's. 

You only have to sneeze on them to double the power figures. 

Edited October 29, 2017 by Timmyb