Mazda DISI Proves Timing is Everything

The Ward’s 10 Best Engines competition celebrates 13 years of recognizing outstanding powertrain development. In this fifth of a series, Ward’s explores Mazda’s power-packed 2.3L turbocharged direct-injection gasoline I-4. Watch for features on the other 2007 winners throughout the year.

The cliche says timing is everything. If that’s the case, Mazda Motor Corp. couldn’t have planned it better, launching a downsized alternative to ever-larger V-6s just as U.S. gasoline prices began what appears to be an irreversible upward climb.

Engine downsizing is a phenomenon industry powertrain pundits had been predicting at least a couple years before Mazda introduced its punchy DISI (Direct Injection Spark Ignition) 2.3L turbocharged DOHC I-4 for the Mazdaspeed6 in late 2005.

But downsizing done improperly – particularly in the displacement-addled U.S. market – can be a recipe for customer dissatisfaction that erases any of the desired fuel-economy benefits.

No danger in that department for Mazda’s percussive 2-time Ward’s 10 Best Engines award-winner: Performance is never an issue, considering the tamest specification of the DISI 2.3L – in the Mazda CX-7 cross/utility vehicle – develops 106 hp/L.

And the specific output numbers get larger, to 114 hp/L in the Mazdaspeed3 and 119 hp/L in the Mazdaspeed6.

So Mazda has blessed itself with a genuine alternative to thirsty, large-displacement V-6s that gives up nothing in customer-pleasing performance and generates a tangible fuel-economy gain.

Robert Davis, Mazda North American Operations senior vice president-product development and quality, told Ward’s last year the high-tech DISI 2.3L 4-cyl. might, in fact, be better than a 6-cyl. engine to support the brand’s beloved “Zoom-Zoom” tagline.

Equally important, “Direct injection for gasoline engines will remain one of Mazda’s core environmental technologies,” says Noriyuki Iwata from Mazda’s powertrain planning department.

He adds that the trend toward engine downsizing is on the upswing, particularly in Europe, another region where the 2.3L DISI also plays an important role in Mazda’s product range.

European drivers, who long have endured lofty gasoline prices, are no less willing than their U.S. counterparts to sacrifice performance in the name of efficiency.

Iwata says outstanding performance was a design priority for the 2.3L DISI 4-cyl., a variant of the MZR DOHC I-4 engine architecture developed by Mazda and used extensively throughout its and part-owner Ford Motor Co.’s model ranges.

“In turbocharged engines, the utmost attention must be paid to achieving levels of acceleration that allow one to feel the joy of driving,” he says. “Because of this, in terms of (components) and systems, we concentrated on choosing the best turbocharger and finding the optimal intake setup. We also took advantage of the direct-injection characteristics to improve the response.”

Powertrain engineers and developers have found direct-injection gasoline (DIG) technology an ideal compliment to turbocharging. DIG typically helps an engine generate improved low-rpm torque, a perfect companion for turbocharging systems, which often cannot produce satisfactory power at lower engine speeds due to turbocharger “lag.” Before the advent of DIG, downsized felt downsized – particularly when accelerating from a standstill.

DIG is a boon for small, turbocharged engines, and in the case of the DISI 2.3L’s engineering, Iwata gives a particular nod to Mitsubishi Electric Corp., which developed and supplies the unique fuel injectors for the 2.3L DISI’s fueling system.

Some reviews have said the 2.3L DISI is not particularly stingy with fuel.

“The fuel efficiency is better than a V-6 engine with similar power output,” Iwata flatly counters.

And Davis says there’s another, less-visible benefit: The 2.3L DISI is markedly lighter than the all-aluminum 3.0L and 3.5L DOHC V-6s Mazda uses in various models. The lighter DISI 4-cyl. enhances handling and steering feel, important dynamic attributes for Mazda.

Ward’s 10 Best Engines judges have noted a difficulty with DIG engines seems to be in generating satisfying intake and exhaust sounds, especially at startup.

Engineers agree DIG – particularly when augmented by one or two turbochargers – can present challenges to producing a performance-rich soundtrack, either on the intake or exhaust sides of the engine. But many believe new technologies and better understanding of the systems will improve DIG engines’ sound “signature.”

Mazda’s 2.3L DISI has not been acclaimed for its exhaust note, but Iwata says opinion regarding intake and exhaust “quality” can be highly subjective.

“I think different people have different tastes, and I hope people enjoy the unique sound of the turbo engine,” he says. “As for the future, I can say that our R&D efforts will continue (to improve DIG engine sound quality).”

The last two years have seen several production engines adopt DIG, although the combination of DIG and turbocharging is more prevalent for 4-cyls. rather than V-6s, which often have enough displacement to negate the need for turbocharging.

Iwata says developers for the DISI 2.3L 4-cyl. benchmarked mainly European auto makers’ engines.

Given its high-performance power and torque ratings, the DISI 2.3L DOHC I-4 already appears to be in a high state of tune, but Iwata says Mazda will not divulge any future planned improvements or enhancements for the engine – despite the fact the MZR architecture now is into its veteran years of production.

Some reports from Japan suggest Mazda is planning a resurrection of its Miller-cycle design for smaller-displacement engines.

The Miller-cycle – which delays closing of the intake valves to reduce the engine pumping losses that hinder efficiency – was last used by Mazda in North America in a supercharged 2.3L DOHC V-6 for the low-volume Millenia S sedan, which was discontinued in 2002.

Nor will Iwata or other Mazda sources comment on whether the auto maker will take the lead on development of Ford-family 4-cyl. engines in the future.

It is possible Ford may draw on its European operations for expertise in smaller-displacement engines, although Mazda’s MZR design has enjoyed a reputation for durability and refinement, as well as respect among enthusiasts. Mazda’s seminal MX-5 roadster, for one, uses a 2.0L variant of the MZR.

Although Iwata will not comment directly on Mazda’s future engine-development plans for MZR, or its replacement, he does say much of what is on display with the award-winning DISI 2.3L turbocharged I-4 is earmarked as a foundation for the company’s powertrain direction.

“Direct injection for gasoline engines will remain one of Mazda’s core environmental technologies, and we believe direct-injection technology will be one of the main environmental technologies of the future,” Iwata says. “As well as this, we think diesel-powered cars are also a good choice.”