Hyundai Motor Co. on Tuesday unveiled its first direct-injection gasoline engine, saying it delivers more power with a 10 percent improvement in fuel economy.

The 2.4-liter engine, called the Theta II, will debut in the redesigned Sonata sedan, due in U.S. dealerships early next year, Hyundai said in a release.

The automaker spent four years and 170 billion won ($147.4 million) developing the new powerplant as part of its push to become a leader in fuel-efficient cars.

Hyundai said it will introduce direct-injection technology across its range of gasoline engines and mount them on other models. The technology boosts mileage by improving combustion.

Compared with conventional engines of equal displacement, the Theta II delivers 7 percent more torque at low revolutions and 12 percent more at the high end. It also improves mileage by around 10 percent, the South Korean carmaker said.

Hyundai eked out further gains by incorporating dual continuously variable valve timing to improve air intake and exhaust. This technology adjusts the length of time the engine valves are open or closed to maximize power and reduce emissions.

The Theta II also employs a three-stage variable induction system that automatically regulates the volume of air sucked into the combustion chamber for optimal air-to-fuel mix.

In addition, weight-saving measures boost the engine's overall performance, including a reinforced bulkhead that allows for a stiffer engine block without added weight. Hyundai says it also reduced the weight of the crankshaft and catalytic converter, partly by using thinner steel.

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