Honda Unveils Fuel-Efficient, Powerful Engine : Autos: The revamped ’92 Civic will be equipped with the new engine, which is rated at 48 m.p.g. in the city.

In another Japanese technological advance, Honda Motor Co. unveiled a new car engine Tuesday that observers described as a breakthrough that achieves higher horsepower and fuel economy at the same time.

Honda said the engine will be available in the 1992 Honda Civic to be introduced in the United States this fall, marking the first mass production of the technologies it employs. Engineers said the engine is impressive not for sheer fuel economy but for combining fuel efficiency with enough power to propel four-passenger cars and meet U.S. and California emission standards, all in an affordable car.

Honda’s U.S. officials said the upcoming Civic, an all-new car replacing a somewhat dated version, will be rated by the U.S. Environmental Protection Agency at 48 miles per gallon in the city and 55 m.p.g. on the highway when equipped with the new engine.

Although 48% better than the current Civic, it is 10 m.p.g. less than a Honda executive told Congress earlier this year that the new Civic would get. It is also below the current fuel-economy leader, the Geo Metro, a Japanese-built car sold by General Motors, which is rated at 53 m.p.g. in the city and 58 on the highway. But the Civic is a larger car.

“I think it’s a pretty significant leap,” said Csaba Csere, technical director at Car & Driver magazine, who has driven the Civic equipped with the new engine.

“It does indeed provide a combination of performance and fuel economy at levels we haven’t seen before. . . . I don’t think there’s anyone in Detroit who can do this.”

The technologies--a combination of “lean burn” air-fuel ratios and engine valves that automatically open or close as needed--have been researched for years. But among other problems, manufacturers have been unable to meet U.S. emissions standards, not to mention the more stringent California regulations.

“This is technology being evaluated by manufacturers worldwide,” said Gary W. Rogers, president of FEV of America Inc. in Southfield, Mich., a subsidiary of a German firm deeply involved in such research for European auto firms.

“If Honda has a completely variable valve-timing system, they will be the first to bring it into mass production. What’s significant is that they’re going to sell it in the United States, which suggests they’ve made some milestones on emissions.”

Chrysler Corp. and Ford Motor Co. had no immediate comment about Honda’s claims, but General Motors voiced skepticism.

“We’ve evaluated lean burn engines for years, and pertinent questions remain. That is, what kind of catalyst has been developed to handle the different emissions patterns that result from using that technology?”

GM was referring to the fact that the current three-way catalytic converters in use in this country to combat emissions will normally operate properly only at a 1-to-15 ratio of fuel to air in the engine’s combustion chamber.

But Honda’s new engine boasts a 1-to-25 ratio. Car & Driver’s Csere said Honda has achieved such a lean burn that the inherent emissions fall below U.S. and California minimums.

In an apparent coincidence, Mitsubishi Motors also announced a major advance in automotive fuel economy Tuesday, reporting similar performance in an engine similar in size, to be mounted in its Mirage model cars this fall.

But Mitsubishi didn’t make the same performance claims as Honda. According to Car & Driver, the new Honda can reach 60 miles per hour in about 10 seconds, unheard of in super-efficient engines.

“What we have done is to improve fuel economy without sacrificing performance, driveability and reliability,” said Nobuhiko Kawamoto, president of Honda.

It remains to be seen how many of the high-mileage cars can be sold, Honda officials acknowledged. As gasoline prices have remained near historic lows, fuel economy has fallen on the list of U.S. customer priorities.

In testimony opposing tougher federal fuel economy standards earlier this year, a Honda executive describing the upcoming Civic to a Senate committee complained that the car will probably account for less than 1% of its U.S. sales.

While the Honda fuel economy rating is based on the test of an actual automobile, the Mitsubishi ratings are estimates based on computer analysis. Both engine designs, however, are based on the principle of improving the engines’ air-to-fuel ratio.

Honda said its new technology generated 235 new patents and involved a complete redesign of its engine, using technology from the Honda F-1 racing car as well as such tools as the company’s Cray supercomputer.

In the conventional four-cylinder engine, air and fuel are injected into each of four combustion chambers. The air in the chamber is compressed by a piston that slides up a cylindrical tube and the mixture of fuel and air is then ignited. The explosion in the chamber pushes down the piston and powers the car.

The trick, says Hideyo Miyano, Honda’s director of research, is to reduce the fuel in the mixture without reducing the speed and heat at which the mixture burns. If it burns too slowly, performance is lost, whereas if it does not burn hot enough, the engine probably will release more pollution.

Peering into the combustion chamber with laser photographs to analyze the activity, Honda’s engineers discovered that if the air and fuel were drawn into the chamber in such a way that it created a swirl rotating at a preset speed, the two elements would mix more quickly and burn more efficiently.

Honda redesigned its engine making the crown of its piston dish-shaped to encourage the swirl. With the help of an air/fuel sensor developed for Honda’s F-1 race car, the engine regulates the mixture going into the combustion down to precise levels.

As a result, Honda was able to push the fuel to air ratio to one part fuel to 25 parts air. That is a substantial gain over the 1 to 15 ratio now common in conventional cars; the “lean fuel” mixture accounts for the improvement in fuel efficiency.

Leslie Helm reported from Tokyo, and Donald Woutat reported from Detroit. Times staff writer Amy Harmon in Detroit also contributed to this story.