Detroit — The 1983 Ford Thunderbird, at a steady 50 miles an hour on the road, requires 6.2 horsepower. In contrast, the 1982 T-bird it replaces requires 12.
Obviously aerodynamic horsepower, as it is called, does not yield fuel-economy gains equal to the reduction in required horsepower at that highway speed. But even though the weight reduction in the coming Thunderbird is small - less than 100 pounds - the gain in fuel economy should be in the area of 10 to 15 percent.
And that gain will be almost completely the result of shape and styling. When engineers here are measuring gains in fuel economy in teaspoonfuls per tank, as they are now, that's a whopping increase.
Indeed, dramatic improvements are coming in fuel economy from a virtually unexpected quarter: styling.
Automotive executives have talked for decades about how important styling is. Now some strong and truly impressive gains in miles per gallon are being designed into cars by making them more aerodynamic so they're slicker as they move through the air.
The key to understanding aerodynamic drag lies in understanding that any object moving through the air - car, airplane, or brick - encounters resistance from the air. Certainly the larger the object, the more drag.
''You can make a brick aerodynamic if you handle the corners properly,'' says Jack Telnack, chief design executive for Ford Motor Company. He is only half joking.
An old example can be found on many breakfast tables. The conventional sugar cube, well under an inch on each side, will encounter about as much resistance when moving through the air as a vastly larger egg, assuming the egg is moving through the air with the large end first.
Interest in aerodynamics isn't new. Several years before the start of World War II Chrysler took a 1932 DeSoto and mounted the body backward on the chassis. The car normally had a top speed of 75 miles an hour, but mounted with the more aerodynamic rear forward it handily topped 80 miles an hour.
Even that comparison tells something. Today the emphasis is on fuel economy, whereas in the days before the energy crisis only top speed really mattered.
If an automaker were to repeat Chrysler's old work today, it would undoubtedly be criticized on grounds of safety. But the change in top speed illustrates how realistic aerodynamics really is.
In some ways aerodynamic changes on cars are obvious. The front air dam is one. It's the part, usually plastic, which is seen hanging below the front bumper of race cars. Today it's common on many cars.
The new hot-selling and strikingly designed Chevrolet Camaro and Pontiac Firebird, for example, have pronounced air dams.
Others are far more subtle. Take the mounting of side and rear windows, for instance. There's a major push on at all car manufacturers these days to mount the windows flush on the outside. That means that when you run your hands from metal to glass at the side or top, the glass is indented to the very minimum.
The change is tricky to see. But if you look closely and compare 1978 or '79 models with 1982 and '83 models, you'll notice it for sure.
At times the subtlety is almost subliminal, as in the Ford Escort. If you'll notice the line where the front end, just above the bumper, ends and the hood begins, you'll see that the hood has a pronounced bend forward.
When testing the Escort in a wind tunnel, Ford found that a real decrease in aerodynamic drag is possible by moving the front edge forward.