TOKYO -- Nissan Motor Co. thinks U.S. car buyers will stick with V-6s if those engines provide both performance and better fuel economy. And it thinks its revised series of high-revving 2.5- and 3.5-liter "VQ" engines will fill that bill.

The engines will be offered on the 2007 Infiniti G35. The Altima will get one of the new VQ engines.

U.S. car buyers have been favoring four-cylinder engines in recent months because of $3-per-gallon gasoline. But long-term, "The six-cylinder market isn't shrinking," predicts Yo Usuba, Nissan's senior vice president in charge of the powertrain engineering division.

Nissan's current engine lineup is split this way: 50 percent four-cylinders, 25 percent V-6s and 25 percent V-8s and diesels. Nissan executives say they don't expect that to change.

"A V-6 still offers value to the customer," especially in performance, says Toshihiro Hirai, senior manager in the powertrain planning group. Nissan's plan is to improve the fuel economy of its V-6s rather than move customers to four-cylinder engines, he says.

The new V-6s offer a 10 percent improvement in fuel economy over the current VQs, Usuba says. That's mostly the result of reduced friction and improved intake and exhaust.

Usuba cited in-house tests of combined city-highway driving but would not provide specifics.

The engines also boast much higher power performance. Usuba didn't give horsepower data, but the engines are expected to offer at least 300 hp, up from 280 hp on current engines.

The new engines peak just shy of 7,000 rpm, compared with around 6,000 rpm for Nissan's current V-6s. The engine can rev up to 7,500 rpm, compared with a bit less than 6,500 now.

That gives the engines considerable power at all speeds, particularly when merging on highways. Nissan says acceleration from 0 to 62 mph is one second faster than with current V-6s.

Production of the new engines began in July at Nissan's plant in Iwaki, Japan. Nissan spent ¥10 billion, or $85.9 million at current exchange rates, refurbishing its No. 2 line there for the new engines.

The VQ series has been among Nissan's most successful engines. The company currently makes about 800,000 VQ engines a year. That is almost a quarter of its annual engine output of 3.5 million. It expects output of the new family of VQ engines, including the 2.5- and 3.5-liter ones, to reach 1 million a year.

The new engines are known as the VQ25HR and VQ35HR. The "HR" stands for "high revolution" or "high response." They were designed specifically for use in rear-wheel-drive cars.

They are the first in a new VQ family which later will include engines for front-wheel-drive cars, too.