By Yoshio Takahashi Of DOW JONES NEWSWIRES

TOKYO (Dow Jones)--A Nissan Motor Co. (7201.TO) engineer said Tuesday that a gasoline-electric hybrid version of its Fuga sedan will likely be up to 90% more fuel-efficient than the gasoline-powered version.

"We expect (fuel economy) to improve by 60%-90%" over the conventional model, Koichi Hayasaki, a Nissan chief engineer, told reporters at a media briefing on the company's new power-train technology.

The remarks give the first indication of the fuel efficiency of the Fuga hybrid, which is Nissan's first gasoline-electric model sold on a full-scale basis using the company's own hybrid technology.

Nissan, Japan's second biggest car maker by volume, will roll out the Fuga hybrid this autumn in Japan and next year in the U.S. The model will be driven by a 3.5 liter V6 engine and an electric motor.

Nissan is strong in electric cars, but the company has fallen behind rivals such as Toyota Motor Corp. (7203.TO) in the hybrid car segment. It currently sells only its Altima hybrid model, which uses Toyota's hybrid technology.

Hayasaki said Nissan's own hybrid system will be about 30 kilograms lighter than Toyota's system, helping its cars to consume less gasoline. Nissan's system uses one electric motor whereas Toyota's uses two.

The engineer also said the cost of Nissan's hybrid system should be lower that those of Toyota's due to its simpler structure, though he declined to elaborate.

The hybrid Fuga could run up to 19 kilometers per liter, as the gasoline engine version goes about 10 kilometers per liter, he said.

The official fuel-efficiency of the car will be determined after testing, a Nissan spokesman said.

The new model will enhance the company's line up of green cars, as it joins the Leaf electric hatchback which will debut late this year. The Fuga is known as the Infiniti M model overseas.

Hayasaki said he wants the new Fuga to perform better than the hybrid version of Toyota's Crown luxury sedan, which can go 14 kilometers to 16 kilometers per liter, and the Lexus GS450h, which goes 14 kilometers per liter.

Nissan aims to almost double the fuel economy of its new Infiniti M luxury sedan with a hybrid version due out in 2012. Engineers at the Japanese automaker have been working hard on a new type of hybrid system for half a decade, preparing it for use in the upcoming M35 Hybrid.

The new setup uses one electric motor and two clutches, making it far less complex than Toyota’s current setup and also much cheaper. According to Nissan’s top rear-wheel drive hybrid engineer Koichi Hayasaki, the company’s new hybrid system does away with the need for a torque converter by using a lithium ion battery and the two-clutch setup – something he says other automakers believed was a hurdle that couldn’t be cleared.

As a result, “We’re aiming for an improvement of 60 to 90 percent,” he said, a significant improvement over the 30 percent improvement produced by full hybrid systems like Toyota’s or the 15 percent improvement by mild hybrid systems like Honda’s.

Another benefit of Nissan’s simpler hybrid system is its weight. The less complex system is not only cheaper but should come in at roughly 66 lbs less than a comparable Toyota setup.

Currently the new Infiniti M37 is rated at 18/26-mpg (city/highway).