DETROIT (AP) — To improve gas mileage, automakers are tweaking cars and trucks between model years, especially in the cost-conscious and popular market for sedans.

Honda Motor Co. recently announced changes in its Accord sedan that boosted highway mileage by almost 10% from the 2010 to 2011 model years. Most automakers change model years late in the summer.

With the Accord, engineers improved the car's aerodynamics, reduced engine friction and changed the top gear in the automatic transmission to boost highway mileage from 31 to 34 mpg and city mileage from 21 to 23 mpg, Honda said in a statement.

The Accord, the second-best selling car in the U.S., moved from near the bottom of the midsize pack to second place in gasoline-powered highway mileage. It was bested only by Hyundai's Sonata at 35 mpg.

The moves come as automakers increasingly use advanced technology to raise fuel economy with their internal combustion engines. Many have made four-cylinder engines as powerful as older six-cylinder motors. They're using transmissions with six or more speeds, direct fuel injection and tires with less resistance.

Honda changed the Accord's transmission so the motor works less at highway speeds. It used thinner oil to decrease friction in internal parts, and it changed the floor panels to make air flow more smoothly beneath the car, said spokesman Jon Fitzsimmons. It also reduced the rolling resistance on the tires.

At Hyundai Motor Co., executives decided early on not to offer the new 2011 Sonata with a six-cylinder engine, saving 50 to 100 pounds of weight that helped boost fuel economy, said John Krafcik, chief executive officer of Hyundai Motor America.

The company instead designed a new four-cylinder engine with technology that directly injects fuel into the cylinders surrounding the pistons. It uses less fuel and generates more horsepower than conventional engines. Other automakers also either are using the technology or are working on it.

Customers shopping for midsize cars generally have families and need space for children, yet they are budget-conscious, Krafcik said.
"For the folks who are staying in sedans, they tend to put a real premium on fuel efficiency," he said.

Chrysler Group LLC, which is at the bottom of the midsize pack in fuel economy with its Dodge Avenger and Chrysler Sebring models, is in the midst of improving them for the 2011 model year. It promises significant improvement in gas mileage, although the company will not give numbers yet.

The reworked Sebring and Avenger are due out in the fourth quarter of this year. They now get 21 miles per gallon in the city and 30 on the highway.

Ford and General Motors Co. said they did not expect any fuel economy changes in their midsize models. Ford's Fusion is tied with the Accord at 34 mpg on the highway with a four-cylinder engine and automatic transmission, while GM's Chevrolet Malibu is close at 33 mpg.

The 2010 version of Toyota's Camry, the top-selling car in the U.S., gets 22 mpg in the city and 32 on the highway. Figures for the 2011 model were not available Tuesday.

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