Time was when hot-rodding meant getting up to your elbows in an engine and tinkering around with a trusty wench. Not anymore. There are now computers under the hood that regulate everything from ignition timing to fuel mixture.

Trouble is, these tireless black boxes are programmed for the average Sunday driver, making it nearly impossible for shade-tree speed freaks to fiddle with them for peak performance's sake. So determined motor-heads have turned into computer hackers, plugging laptops into the black boxes and rewriting codes to wring more horsepower from stock mills. Sometimes, these folks even do their programming from the passenger seat while somebody else does the driving.

But what about those non-hackers with a need for speed? For them, some enterprising automotive companies have begun marketing souped-up computer chips that can be fitted into the black boxes. Two of the biggest outfits serving this new, $60 million niche market are Fairfax, Va.'s Autothority and Memphis, Tenn.'s Hypertech. Autothority claims that its chip can increase the output of a Mazda Miata's four-cylinder engine by 15 horsepower; Hypertech says that its chip can pump up a Chevrolet Camaro's V-8 by up to 40 horsepower.

In the old days Hypertech manufactured racing camshafts. "Now we're software engineers," says marketing director Godfree Roberts.