MARTINSVILLE, Va. (AP) – NASCAR says the exhaust problem in its Car of Tomorrow is a simple fix.

Several drivers finished the race with a “carbon monoxidey feeling,” some after their exhaust systems failed during the race, Nextel Cup director John Darby said.

Brian Vickers suffered second degree burns to his feet, and needed oxygen after Sunday’s race because of his exposure to the carbon monoxide.

“The exhaust failure is the first thing we went to work on,” Darby said before practice Friday at Martinsville Speedway, where the COT will race again this weekend.

NASCAR determined teams used a thinner metal for their exhaust systems in the COTs than they typically use in the cars, and the heat generated during the race caused several of the pipes to break. Some also misapplied the padding designed to shield other components from the heat, and that caused other parts to fail, Darby said.

“When a problem and the reason for the feeling is so obvious, then it becomes a pretty simple fix,” he said, referring to the carbon monoxide getting inside the race cars.

Matt Kenseth’s team was among those with a broken exhaust pipe, and he said the heat melted the protective foam inside his door. The fumes made him sick all week.

Vickers and Denny Hamlin also were left feeling sick after the 500-lap race, but NASCAR did not feel like it needed to mandate that the exhaust systems be heavier.

“The one thing I do know is there’s a whole lot of really smart people out there,” Darby said. “If they failed an exhaust system last week, chances are they’re not going to fail it this week.”

Hamlin said his exhaust failed in practice, was replaced and was still intact when the race ended. He said the best guess he could make was he felt sick because Bristol’s bowl shape keeps fumes close, and the temperatures were high, too.

Other than that, Hamlin said, he embraces the switch to the COT.

“For the most part, I think it’s a change for the good,” he said, adding that in two weeks, the cars are already starting to look more like the normal race cars.

Hamlin said he also has looked into using oxygen tanks to clean out his system, especially during short track weekends, to help flush out any carbon monoxide. Jimmie Johnson has made oxygen a part of his routine at Martinsville for two years.

“There are a lot of things that breathing oxygen helps you with,” Johnson said. “One of the most important things, especially after a short track, is to get the carbon out of your system. All the exhaust fumes, brake fumes, everything you ingest in the course of a race. Pure oxygen is the only thing that will get that out of your system.”

Beyond exhaust, the other big COT issue came when Greg Biffle’s car failed postrace inspection because it was too low, and NASCAR declined to penalize him this week. Instead, it studied Biffle’s car this week and determined the back end had settled because of normal race wear and tear.

Robin Pemberton, NASCAR’s vice president of competition, said the view from the officials tower at Bristol highlighted several features of the cars, which are being developed to improve driver safety and somewhat level the economic playing field.

While regular NASCAR racers normally lift when bumped from behind, causing them to spin and often hit something, the COT seemed to absorb the impact better, Pemberton said, which suggests fewer cautions will result from normal bump and grind racing.

Darby said walking through the garage at Martinsville, it is apparent already that teams have made modifications for this week based on what they learned last weekend.

In the end, he added, on race day, it’s still all about the competition.

“This comes from the drivers that are still maybe on the negative side as well as the ones on the positive side, the one thing that they all agree on is if that’s what’s out there on Sunday, then we’re going to jump in the thing and race it,” he said.