About a year ago Ralph Moody, a legendary stock car driver and mechanic, was thinking about retiring. "All I wanted to do," he says, "was a little bit of nothing." Today Moody has postponed the rocking chair in favor of rocking the auto industry. He and a pal have designed a car with an engine that gets up to 84 miles to a gallon of diesel fuel. The Moodymobile, as it's called, came out of the Oak Hill, Fla. auto shop of Mike Shetley, whom Moody knew from their days together on the Ford racing team. Shetley had summoned his old boss from his Charlotte, N.C. home to help with a complicated chassis for a Thunderbird replica. Moody, 60, solved the problem in a week, and soon the men were talking about building a sports car with a diesel engine. "The idea wasn't high mileage in the beginning," says Shetley, 36. "We wanted a nice-driving car for the guy who couldn't afford luxury."

What they did was modify, inside and out, a four-cylinder Perkins diesel engine (like those used in motorboats) and drop it into a 1979 Capri body, adding a turbocharger for extra power. (The turbocharger reroutes hot exhaust gases that normally escape from the tail pipe.) The Moodymobile was soon stirring interest locally and was test-driven by Congressman Bill Chappell. He immediately wired President Carter: "I've seen it, I've driven it and it works."

A fortnight ago Moody and Shetley drove the car 850 miles to Washington, D.C. (on 11.1 gallons of fuel) and testified before the Senate Energy Committee. The car (which is noisier than a conventional one) faces a stiff battery of environmental tests before it can be marketed, but Moody is confident one of the big automakers will buy the rights to the patent. Ford, Chrysler and General Motors have all expressed interest.

Born in Massachusetts, Moody raced midget cars as a teenager and in 1956 joined Ford, later becoming chief mechanic. That meant giving up competitive driving. "I could still outrun them," he proclaims. "I did all the test work." Champion drivers like Mario Andretti, A.J. Foyt, Cale Yarborough and Bobby Allison have won with Moody-groomed Fords. He also designed much of the safety equipment now standard in stock cars.

When Ford stopped racing in 1971, Moody opened a small "speed shop" in Charlotte (a city he, his wife Mitzi, 53, son Ralph III and daughter Ann have lived in for 23 years). He began selling race cars to drivers and, as a sideline, refined a gasoline engine that gets up to 65 miles per gallon. "We put it on the shelf," Moody shrugs. "Nobody needed it then."

Shetley claims—perhaps extravagantly—that they have turned down $100 million from Arab interests to buy rights to the Moodymobile, which has cost them $20,000 to develop. Meanwhile, the designers are filing away in cardboard boxes the names of private citizens eager to place orders. Possibly 2,000 of the cars will be available late this year for about $7,000 apiece. And for the time being, Ralph Moody has put off retirement. "In the old days on the racing circuit, I worked day and night," he smiles. "Now it's only 20 hours a day."