Dayton Beach, Fla. ? In the good ol’ days at the Daytona 500, a security guard would poke through Dave Roberts’ motor home, checking to see if he was trying to sneak friends into the race.

Now, the guard comes through with a dog — searching for bombs.

Indeed, America’s heightened security is having an impact in even the most carefree of environments: the beer-swilling, fun-loving home of debauchery known as the Daytona infield.

With the nation on high alert for terrorism this weekend, officials at Daytona International Speedway took extra precautions to protect their packed crowd of an estimated 200,000 for Sunday’s big race.

“I had friends who told me not to come here,” said Roberts’ wife, Denise. “I told them I had to. If they let us change our lifestyle, then they’ve won.”

So, the party carried on, albeit with more than a few eerie reminders of the realities.

Bomb-sniffing dogs checked motor homes, and hundreds of policemen and security staffers used mirrors to check under cars for explosives.

Once inside the track, hundreds of people living in the makeshift tent cities saw police circling their living quarters every few minutes.

Although Army Blackhawk helicopters flew over the track repeatedly in the days leading up to the race, officials insisted they were merely rehearsing for a flyover as part of prerace pageantry.

There wasn’t much else flying overhead. The Federal Aviation Administration restricted noncommercial aircraft within three miles around and 3,000 feet above the track.

Track officials were guaranteeing a thorough security sweep. People noticed.

“I’ve never seen such tight security in a big arena like this,” said Daytona 500 grand marshal John Travolta, who went to the Super Bowl and World Series in the past year. “I don’t think I’d bring my family here if it wasn’t safe.”