Michael Taylor: Mazda’s Miller Cycle

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It feels like a lifetime ago that Mazda introduced the Miller cycle in the Millenia. The Miller cycle, Mazda said, would revolutionize the way everyone built their combustion motors.

In the years that followed, the Millenia and its KJ-ZEM V6 Miller cycle engine were met with such an unenthusiastic response from customers that, by 2003, Mazda had run a tsurugi through the whole thing.

Mazda struggled to explain to journalists, much less its customers, what the oily, whizzing bits were doing, but even when it tried, its efforts focused on the wrong bit.

As a journalist of the era, I know that no one had preconceptions about the Miller cycle, but we got stuck on the supercharger. Superchargers, you see, were thought of as stuff the Yanks used in ’70s and ’80s hot rods and, as such, were a bit old hat. So that’s what most of the criticism was aimed at.
If they thought of the Miller cycle at all, the wider public got it confused it with the Atkinson cycle, which, as everyone knows, is a low-carbohydrate, high-protein fad combustion process popular in the early 2000s.

The other problem for journalists assessing the technology was that we couldn’t take Mazda’s claims to have unearthed The Next Big Thing in combustion power seriously, because not even Mazda did.

Mazda’s V6 engine department received an extra-large box of engine darts from Secret Santa in the mid ’90s and every engineer was hurling handfuls of them, willy-nilly, at an ‘approved program’ dartboard, then waiting for a promotion to the board. They brought out a 1.8-liter V6 that was so small you had to get it serviced at the jewelers. There was a 2.0-liter V6, a 2.3-liter Miller cycle V6, and a pair of 2.5-liter V6s, neither of which shared anything of value with the other. There was also a 3.0-liter and a 3.5-liter V6, just for giggles.

The company even had V8 and V12 atmo engines that were developed, validated and tooled up to production readiness before being shelved when the juicy profits of the luxury world never came.

It just felt to outsiders like Mazda was developing vee engines for a laugh (it had another dozen or so four-cylinder engines as well, plus commercial diesels), rather than with an aim of making money, and so it was proved, with Mazda going so close to drowning that Ford had to bail it out.
To Mazda’s great surprise, the company famous for one oddball, unique, expensive, weird-sounding engine technology couldn’t afford a second one. But the trouble wasn’t the Miller cycle technology. It was that the V6 Miller cycle got lost in the fog of Mazda V6s and no one followed them down the technology path.

So it was stuck on its own, Miller cycling away for a decade with a raspy, crunchy-sounding combustion process. There was no hive mind working on the problem like there is today.
Subaru finally thought it was a good idea and bunged it into the B5-TPH concept car in 2005, but didn’t put it into production. Saab came at the problem a different way, and came up with a variable-compression engine that no one put into production for many reasons.

But here we are in 2022, a full 20 years since Mazda killed the 2.3-liter Miller cycle V6, and Miller cycle engines have finally gone mainstream.

The main reason is that they’re a shortcut to cleaner emissions and every gram an engineer can shave off these days is worth approximately US$500 of heavy, consumer-oriented comfort that the product planning people can convince customers they need, thus neatly offsetting all that engineering work.

Volkswagen has Miller cycle engines in everything from the Golf to the Polo. BMW has just put one in the 740i limousine, after ironing out all the unsophisticated sounds Mazda stumbled across.
So Mazda has gone back to the Miller cycle, right? Err, no. Mazda has learned its lesson from going it alone on combustion technologies by, well, using another combustion process no one else uses.
At least Mazda is always interesting to watch.

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