Mark Martin, easily outrun in the Detroit Gasket 200, was given the victory nearly two hours after the race Saturday when NASCAR relegated Dale Jarrett to the rear of the field because of an unapproved engine part.
"The intake manifold had been modified externally on the carburetor mounting flange," NASCAR spokesman Andy Hall said. "It was a part that did not conform to NASCAR rules."
Jarrett was relegated to 42nd after a post-race inspection of his Ford Thunderbird at Michigan International Speedway.
It was the second time that a Busch Grand National victory was taken away from a driver. In May 1992, Jeff Burton was moved to the rear of the field when the post-race teardown revealed his car had a rear end that did not conform to specifications.
The infraction cost Jarrett about $23,000 in earnings, but Hall said no other penalties were assessed.
Neither Jarrett nor Martin could be reached for comment.
In beating Martin by nearly seven seconds, Jarrett ran the fastest NASCAR Busch Grand National race in history, averaging 169.571 m.p.h. The fastest previous race was a 500-kilometer event on July 23, 1994, won by Ken Schrader at Talladega, Ala. He averaged 167.473.
The race around the high-banked, two-mile oval was only the fourth in Grand National history to be run without a caution flag.