Hyundai Motor Co. Ltd. will debut a new version of its 4-cyl. Theta gasoline engine in the refreshed Sonata sedan in the U.S. in February, a Hyundai official tells Ward's at the Tokyo motor show.

Lee Hyun-soon, president-research and development, declines to divulge specifications but says the “power increase will be significant” and there will be an improvement in fuel economy.

The current 2.4L 4-cyl. Theta in the Sonata makes 162 hp and 164 lb.-ft. (222 Nm) of torque. Lee says he is unaware of any criticism of Hyundai's version of the Theta, the so-called “World Engine” because it is shared with Chrysler LLC and Mitsubishi Motors Corp. However, Hyundai led the development of the mill.

Chrysler's version of the Theta, available in the Dodge Caliber compact car and other models, has been criticized for a lack of refinement. But Lee says Chrysler's tuning likely is the culprit.

“If they were trying to generate more power out of the engine, better acceleration feel, (refinement) can be lost,” he says.

As for the Sonata in the U.S., a Hyundai spokesman says the auto maker is committed to the vehicle and the refreshed version should improve sales. Hyundai recently announced it would temporarily halt the car's production at its Montgomery, AL, plant due to high inventories.

The spokesman says the fiercely competitive midsize-sedan segment in the U.S. is to blame for the sales falloff. The current-generation Sonata debuted in 2005 as an '06 model.

Ward's data shows U.S. Sonata sales were down 19.6% through September compared with year-ago.

Other changes to the Sonata include increased use of aluminum, plastics and high-tensile strength steel.