Rodger Penske and Mark Donahue were always looking for ways to gain an edge on the track. During their experiments, they found that dipping the car's frame in an acid bath would erode away small amounts of metal. This had the result of incrementally making their Camaro lighter. One of their Camaros won its last race by lapping the entire field! Needless to say this feat had everyone in the pits talking. At the post-race inspection, it was found that the Camaro was 250 pounds lighter than the 2,800 pound minimum-weight requirement. Mark was about to have his win stripped away, but the story is that Rodger might have hinted that a disqualification could cause Chevrolet to pull its support for the Trans Am series. As a result, Donohue kept the win, but for 1968 the rules were changed to state that all cars would be weighed before the race.
The lightweight Camaro was again used in the 1968 season. The '67 was made over to look like a '68 and then another '68 was built and painted exactly the same. As the story goes, the legal-weight Camaro was put through inspection twice, once wearing the number 15 and again with the number 16. Needless to say, they did well in that race. It's also been said they acid-dipped the body and had to keep people from leaning on the panels as they would have caved in. In fact, they wore vinyl roofs to help hide the waviness from the acid-dipped sheetmetal.
Ahh, the good old days of racing!