For Tom Marx, It’s a 160-M.P.H. Vacation

Driving the streets and freeways of Los Angeles scares Tom Marx.

Five days a week, the 36-year-old drives his late-model Porsche 911 through 18 miles of traffic in 45 minutes to his downtown advertising agency.

“People don’t pay attention,” Marx said. “Most of them are incompetent. They don’t realize the power they’ve got.”

This weekend will give Marx a break from that kind of coronary abuse. He’ll be taking his 1971 Porsche 911 for a 150-mile cruise in just about the same time it takes him to drive from his Van Nuys home to his office.

But Sunday, it will be the safer curves of Riverside International Raceway in The Times/Nissan Grand Prix of Endurance. Marx and co-drivers Jon Winthrop and Larry Amberg will run the 600-kilometer race with speeds approaching 160 m.p.h.

Each member will race a one-hour, 10-minute shift, changing drivers at two scheduled pit stops of about a minute each.

It’s no party out there. It’s a lot of work and expense. Days of testing and racing keep Marx and Winthrop in a perpetual balancing act of careers and budgets. They hardly have time for anything else.

“You can’t do everything,” Winthrop said. “You do business, you go racing . . . “

“And you see your banker,” Marx added with a laugh. “You give up other freedoms in your life.”

“This is going to be one of my major vacations,” he said.

Marx still concedes certain hazards. The Winthrop-owned, 325-horsepower GTU-class Porsche will be racing alongside higher-powered GTO and GTP classes.

“I don’t really have any fear driving on the race track,” Marx said. “You’re out there with people going in the same direction who know what they’re doing.”

Going into Riverside’s tight corners with cars closing at 60 m.p.h. can be tough. “An inexperienced driver can really get into trouble,” Marx said.

There is even more danger now that the race has been decreased from six hours to 3 1/2, inducing drivers to push the cars harder.

“Even though you have to make the car last, it’s a 3 1/2-hour sprint race,” Winthrop said.

“You learn to drive fast and not break anything. You want to be very consistent and run it at 98 or 99%.”

Amberg is renting a third of the car from Marx and Winthrop for $3,000. But it wasn’t just the money that put Amberg behind the wheel.

“He’s a good driver,” Marx said, who has driven with Amberg before.

Three years ago Winthrop came close to winning the GTU class. Working with another team, he took second in the GTU and eighth overall at Riverside.

Getting to that winner’s circle can be a problem for a three-man team: What may be right for one driver may not be for another. Most of the controversy generally is over the car’s suspension.

“You come to a consensus--a mutual decision,” Marx said. “If you can’t agree, you just try something. If it doesn’t work, you try something else. It’s not a science, it’s a lot of trial and error.”