There's neither a nick, scar or speck of grease on Tom Stephens' hands these days, but that wasn't always true.

If the term "hands-on" engineer fits anyone, it's Thomas G. Stephens, vice president and general manager-engineering Operations for General Motors Corp.'s Powertrain Group: He literally grew up taking apart cars and re-assembling them with his own hands -- always tweaking the engines to get more power.

He remains an acknowledged high-performance car nut, but with 16-hour days devoted to developing and leading GM's powertrain strategies -- and two teenage daughters he wants to spend more time with -- Mr. Stephens has scant time to tinker around his garage.

Nor does he find time to spend with a fleet of more than a dozen of mostly vintage GM cars he and a neighbor, a pharmacist who "loves cars," have worked on together over the years and keep in mint condition at an undisclosed location.

Included are such jewels as '66, '67, '70 and '74 Corvettes, a '70 Buick Grand Sport, a 66 Chevy Chevelle, a '79 Pontiac Trans Am and a'64 Pontiac GTO.

Using technical "speak" that only those who truly know their stuff can fully appreciate, Mr. Stephens effortlessly rattles off the most minute specs of every engine, transmission and rear axle ratio of the cars he has restored and that goes for GM's powertrains spanning some 30 years, too.

Then there's his bright red Ford Cobra replicar with the white stripes down the hood powered by "a 427 dual quad engine" he installed himself. It's the only vehicle in his stable that he drives regularly. "The first one we restored (a Corvette) was stolen right after we did it," he recalls, "and that's what got me a little nervous about them."

Describing his Cobra as "a wonderful car -- I'll drive it anywhere, anytime," the red-haired, fully bearded executive says he'd miss the car if someone snatched it "but you'd hate to have them take one of the original Corvettes."

A lanky, boyish looking 47-year-old who'd doubtlessly look more at home wearing coveralls than double-breasted suits, Mr. Stephens' enthusiasm for engines and cars surfaced early.

He grew up near 10 Mile and Van Dyke roads in Warren, MI, practically in the shadow of GM's Technical Center two miles away. It was,a neighborhood populated by like-minded youths. "We were all interested in anything high-performance -- cars, trucks, motorcycles, boats -- you name it. Anything that had an engine that you could take apart and make go faster seemed like it was the thing to do.".

The first car he and his buddies rebuilt was an abandoned 64 GTO they acquired for a $25 towing fee and outfitted with a 427 cu. in. Chevy engine built up from factory parts.

From then on, Mr. Stephens spent most nights for years rebuilding and restoring cars slacking off only during the late 80s when his GM job became increasingly demanding.

As a teenager raised in modest circumstances, his early plunge into powertrains proved to be an expensive hobby, but it also provided invaluable experience. To fund his passion, he worked on a family farm north of Detroit, repaired cars for neighbors and did odd jobs.

Although his pals raced on tracks, Mr. Stephens confined his behind-the-wheel activities to drag-racing because "it was the least-expensive way to go."

Cash became less of a problem after he entered a University of Michigan-Dearborn/GM student co-op program in 1969 and joined GM's hourly payroll working for the Chevrolet Motor Div.

Although at Chevrolet he was getting his first experience backed by GM's mighty resources, ML Stephens and his associates dreamed of one day owning a dealership.

But then a whole new world opened up to him at Chevy. "I worked in drafting, the engine dynamometer area, the Willow Run Assembly Plant, the Milford Proving Grounds -- a lot of different areas."

While other students may have caroused in the university tradition, Mr. Stephens got his nightly kicks another way. "Even when I worked in the drafting room (at Chevrolet), after I was off work I'd go down to the dynamometer room and stay six or seven hours, then go home and start all over the next day. It was a lot of fun. I spent almost a full shift down there along with my full shift upstairs. I was learning; I just loved it. The noise, vibration and excitement were amazing."

Paradoxically, one of Mr. Stephens' primary missions nowadays is to improve noise/vibration/harshness (NVH) characteristics in GM powetrains. "It's a lot easier to make it than to get rid of it," he maintains. Armed with his mechanical engineering degree in 197 1, Mr. Stephens joined GM's Cadillac Motor Car Div. as a junior engineer, moving up to supervisor of product engineering by 1980 and staff engineer-emissions and transmissions in 1982. After that he took on increasing responsibilities at the now-dismantled BOC Powertrain group and at Cadillac, then served two years (1988-'90) managing BOC's Livonia, MI, engine plant.

After a stint as engineering director of the former GM Engine Div., Mr. Stephens landed with GM Powertrain as general manager-engineering Operations when it was formed in 1991. He was elected a GM vice president two years ago this month.

GM Powertrain comes under the aegis of North American Operations (NAO) and is responsible for all powertrains in North America except for Saturn Corp., with which it has a close relationship.

But like everything else at GM, Powertrain is moving increasingly toward globalization, tieing in future powertrain strategies with GM's Adam Opel AG subsidiary in Germany, GM-owned Saab AB in Sweden, GM units in Brazil and Australia, and Isuzu Motor Co. Ltd. in Japan, in which GM owns a 35% stake. Formal powertrain integration between the Opel and NAO reportedly may not be too far off.

"The global opportunity for GM is tremendous," says Mr. Stephens, "and the real opportunity lies in both sides understanding that everybody doesn't have to do everything - that we can work together, that we're all on the same GM team."

While NAO clearly is the leader in V-6s and V-8s, Opel long has specialized in 4-cyl. engines. Indeed, a strong argument can be made that GM has far too many 4-bangers than it needs while overseas units lack NAO's automatic transmission expertise and resources.

The idea clearly is to commonize powertrains wherever possible and still meet customer needs, eliminating costly and time-consuming redundancies - an effort enhanced by GM's new global purchasing strategy, he says. "You could have additional content that you couldn't have otherwise because of common methods and systems," Mr. Stephens observes.

Known humorously as "Mr. Torque Curve" because that's what he considers an engine's single most important spec, Mr. Stephens puts down criticism that GM has stuck with what some describe as "old pushrod technology" to conserve cash.

Reminding that 4-valve overhead cam (OHC) engines with aluminum blocks and heads - technology to which automakers have stampeded in recent years - have been around since 1919, he argues strongly that there's ample room for longstanding, but technically enhanced, overhead-valve (OHV) pushrod technology, based on where and how the engines are used.

"Once we understand what the customer wants, what we find is we need OHV and OVC engines because one or the other won't do it," he says. "You need to have both." Thus, for example, the Cadillac Seville SST has a 32-valve V-8, the Buick Park Avenue Ultra a supercharged V-6 and some entry-level, low-priced GM models with inline OHV 4-cyl. engines as well as 16-valve 4-bangers.

With affordability a mushrooming issue, Mr. Stephens also argues that GM's strategy is sound. He reckons that OHC multivalve V-6 or V-8 engines cost "several hundred dollars more" than OHV engines of the same size. OHV costs drop sharply when applied to inline engines, which includes all 4-cyl. engines and some sixes still being produced, he says.

Affordability - this value equation - is a big issue in the U.S. and everywhere else around the globe, and we have to take it into account when we design our products. "From my perspective, I'm looking for the simplest design that works, that meets customer requirements," he says.

Admitting he may "sound defensive or parochial" Mr. Stephens argues that technology GM uses to develop OHV engines "is every bit as high-tech" as that used to develop multivalve OHC engines.

If GM were to develop a new inline engine, "I'd be in the camp of doing it with OHC technology," he says. But perhaps not without a wrench in each hand.