When he was a NASCAR crew chief, Gary Nelson was known for being able to work in the gray areas of the rule book and incorporate features into his cars that helped his drivers, including Bobby Allison, Darrell Waltrip and Geoff Bodine, win some of NASCAR’s biggest races, among them the Daytona 500.

By 1991, NASCAR itself wanted to take advantage of Nelson’s abilities. Instead of trying to corral him, NASCAR brass hired him to be the director of the series now known as Sprint Cup. Nelson later led NASCAR’s research effort, including the formation of its Research and Development Center in Concord, N.C.

Nelson now is back doing what he loves most — finding ways to build more speed into race cars — and he’s doing it as team manager for Action Express Racing, which will be vying for the Daytona Prototype division championship in this weekend’s Petit Le Mans at Road Atlanta in Braselton.

But the race, no matter the outcome, likely will be bittersweet for Nelson. Saturday’s 10-hour or 1,000-mile race marks the last appearance of the Daytona Prototypes. Next year, teams will switch to a more standardized chassis, making it more difficult to incorporate the kind of technical innovations Nelson is known for.

“I’m sad because all my years in NASCAR, we were welding cars together and building roll cages and suspensions and putting it all together and going to the race track,” Nelson said. “Here in the road racing, I used the same recipe. The cars we race we build ourselves here in our shop with a tubing bender, a welder and a rack full of tubing.

“This weekend will be the last for that style of racing. Beginning in 2017, you have to buy a car from one of four car builders and you’re not supposed to change it much.”

Nelson compared the changes to similar ones he’s seen with NASCAR over the years as rules have made most cars alike regardless of the team or manufacturer.

“We’ll take this last race and do the best we can, then work toward the new system as it comes on line,” he said.

Odds are Nelson will end the season with a championship. Action Express’ two teams are in first and second place heading into the weekend, but the defending Le Mans champion Wayne Taylor Racing team is just seven points off the lead.

Saturday’s race will also be the final one for the Panoz DeltaWing, which was developed in Braselton and will be driven by Katherine Legge, Sean Rayhall and Andy Meyrick.

The GT Le Mans class will have a strong NASCAR connection as well. The Le Mans winning Ford GTs is fielded by team owner Chip Ganassi, who also owns the Chevrolets driven in NASCAR’s Sprint Cup Series by Kyle Larson and Jamie McMurray.

Joey Hand, one of the drivers of the No. 66 Ford, told reporters at a recent test session that his car, which delivered a Le Mans win for Ford on the 50th anniversary of the manufacturer’s first Le Mans victory, should perform well at Road Atlanta. The Braselton course shares similarities with the Circuit de la Sarthe, where the famed 24-hour race is contested.