CC Newsstand: The Triumphant Return Of The Inline Six

2017 Mazda Vision Coupe concept

Just this month, Mazda announced they were developing not one but two inline six-cylinder engines. This news comes after decades of V6 dominance over the inline six (except over at BMW), and in turn the subsequent rise of the turbocharged inline four-cylinder over V6s in everything from German sports sedans to American crossovers. Fans of the inline six layout, widely praised for its inherent balance and smoothness, can rejoice as Mazda isn’t the only automaker to embrace the I6.

Put in context, Mazda’s new inline sixes make sense. Mazda has been slowly creeping upmarket, chasing fatter profit margins that will help insulate the relatively small automaker. Last fiscal year, Mazda’s operating profit fell 43% due to falling sales in China and increased investment in the U.S. dealership network and incentives.

Rather than reattempt a luxury marque like their aborted Amati brand in the early 1990s, Mazda is classing up their regular passenger cars while introducing larger models on a new platform architecture that will use the two engines. One of the two Mazda sixes will be a diesel, dubbed Skyactiv-D, and both are designed to work with the company’s all-wheel-drive system. The new large Mazdas will also be available with a 48-volt mild-hybrid setup and a plug-in hybrid variant.

The gasoline-powered Skyactiv-X inline six will use Mazda’s new spark-controlled compression ignition system, which will first appear on select four-cylinder models and which promises the efficiency of a diesel. For a company Mazda’s size to invest in two new engines and a new platform architecture is surprising but here’s hoping they’re able to get some solid returns on their investment.

Mercedes-AMG GT 53 4-Door Coupe

You can spin a V6 engine off of a V8 engine, albeit not without some technical hurdles. However, with V8s slowly disappearing – they’re supposedly dying, but we heard that back in the ’80s – there’s less of an incentive to develop a V6. Instead, Mercedes and other automakers can spin an I6 off of an I4.

Mercedes-Benz introduced the M256 inline six in 2017 and manufactures it in on the same production line as their four-cylinder engines. The M256 uses the same bore and similar stroke to the four-cylinder engines and is part of a modular engine family that also comprises Mercedes’ inline four- and six-cylinder diesels. To fit this inherently longer engine under the hoods of their vehicles, the 3.0 inline six uses a 48-volt integrated starter/alternator (dubbed ISG) which powers the water pump and A/C compressor, negating the need for belts at the front of the engine bay.

The M256 replaces Mercedes’ V6 engines, returning the Stuttgart brand to the inline six format after an interregnum of almost 20 years. It first appeared under the hood of European S450 models in 2017 and has since proliferated throughout the Mercedes line-up – you can find it in the GLE, CLS and E-Class ranges (with 450 or 53 AMG badging) and in the Mercedes-AMG GT43 and GT53. AMG models also employ an electrically-driven supercharger. There are two different tunes of the M256 – one producing 362 hp and 369 ft-lbs, the other 429 hp and 384 ft-lbs.

A lot of digital ink has been spilled regarding the M256 engine but there’s another inline six in Mercedes’ modular engine family. The OM656 engine, a 2.9 diesel I6, was also launched in 2017 in the S-Class and has since been introduced to the G, E and CLS lines. There are two tunes: one with 282 hp and 443 ft-lbs (in 350 d-badged Benzes) and one with 335 hp and 516 ft-lbs (400 d models). Unfortunately for North Americans, there don’t appear to be any more plans to bring this impressive engine over to the continent.

Like Mercedes, Jaguar Land Rover also has a new modular engine family. Dubbed Ingenium, this engine family comprises inline four and now inline six-cylinder engines. JLR’s “mild hybrid” inline six debuted this year in the Range Rover Sport and, on paper, it looks somewhat similar to the AMG version of Mercedes’ M256. It also displaces three liters, it’s also turbocharged, and there’s a 48-volt electrical system which powers, among other things, an electric supercharger.

The Ingenium six replaces the old supercharged 3.0 V6 and will also appear under the hood of the flagship Range Rover and likely other JLR models. Like Mercedes, Jaguar abandoned the inline six in the late 1990s in favour of V6s. The Ingenium six is available in two states of tune: one with 355 hp and 365 ft-lbs, the other with 395 hp and 406 ft-lbs.

BMW 840d

Unlike Mercedes and Jaguar, BMW never abandoned the inline six. Though its latest UKL platform models eschew an I6 in favor of turbocharged inline fours, BMW makes an I6 available in every other model line. Even the flagship 8-Series can be had with an inline six diesel in some markets.

BMW’s embrace of the inline six has actually spilled over to other automakers. The new Toyota Supra was co-developed with the latest BMW Z4 and they use the same engines – a 2.0 turbocharged inline four and a 3.0 turbocharged inline six, the latter producing 335 hp and 369 ft-lbs.

Not all inline sixes reside under the hoods of sports cars and luxury vehicles. Due to arrive for the 2020 model year in the Chevrolet Silverado and GMC Sierra, the new Duramax 3.0 six-cylinder diesel will produce 277 hp and 460 ft-lbs and be mated exclusively to a 10-speed automatic. GM truck buyers will shell out around $2500 more for the diesel compared to the regular 5.3 gasoline V8.

Though nothing has been confirmed as yet, FCA is allegedly developing an inline six engine dubbed Tornado that may see duty in Ram trucks, among other products. FCA has long offered the I6 Cummins diesel in Ram trucks but discontinued its last gasoline I6, the venerable PowerTech (nèe AMC) 4.0, over a decade ago.

The inline six’s newfound popularity is, for now, confined to rear-wheel-drive and/or all-wheel-drive and predominantly luxury brand vehicles. Though six-cylinder engines have largely disappeared from some segments, such as the mid-size segment, there are still plenty of cars and trucks using V6s. With automakers seeking efficiencies and employing modular platform architecture and engine families, will we see more and more I6s?

Related Reading:

“Mazda aims for upscale appeal with inline-6 engines” – Hans Greimel, Automotive News