YOKOHAMA, Japan — Mazda's new Skyactiv-X engine is a mild-hybrid technological tour de force. But it may be a while before the system shows up in the U.S. market.

Mazda Motor Corp. is still considering how and when to bring the ultra-efficient, high-torque powerplant to its biggest market, engineers working on the next-generation powertrain say.

One problem is the added cost of all its high-tech add-ons. But the bigger consideration is that the current Skyactiv-X engine might not be big enough for U.S. driving needs.

The Japanese carmaker's latest engine technology is currently deployed only in a four-cylinder 2.0-liter gasoline engine that went on sale in the Mazda3 small car last year in Europe and Japan.

The same engine was also deployed in the CX-30 compact crossover for Japan starting last week.

But Eiji Nakai, Mazda's executive officer for powertrain development, said that engine might be too small for the U.S. The U.S. version of the Mazda3, for example, comes only with a 2.5-liter powerplant.

Speaking at a Skyactiv-X test drive here last week, Nakai said Mazda is conducting computer simulations of applying Skyactiv-X technology to engines with bigger displacements.

"We think this Skyactiv-X can be used for larger engine displacement in the future, in line with our product planning," he said. "This technology is applicable to other engine displacements."

Mazda engineer Yoshiaki Yamane said such powerplants could better suit driving habits in the U.S., where drivers prioritize power for high-speed, expressway driving over fuel efficiency.

"Maybe U.S. customers require more power, because fuel economy is not the top requirement," said Yamane, a powertrain engineer who worked on the Skyactiv-X setup.