M6A. Trans-Am Donohue began his Trans-Am series campaign in 1967, winning three of twelve races in a Roger Penske-owned Chevrolet Camaro. In 1967 and 1968, Trans-Am schedule included two of the most prized endurance races in the world, the 24 Hours of Daytona and the 12 Hours of Sebring. Donohue finished fourth at Daytona and won the Trans-Am class at the 12 Hours of Sebring. 1968 would be a banner year for Donohue in the Trans-Am series, as he successfully defended his 12 Hours of Sebring victory by partnering with Craig Fisher and driving his Penske Chevrolet Camaro to victory. Donohue went on to win 10 of 13 races, a Trans-Am series record which would stand until Tommy Kendall went 11 for 13 in the 1997 Trans-Am championship, winning the first 11 races that year in his All-Sport liveried Mustang. Donohue was considered a leading Trans-Am driver of the late 1960s and early 1970s. Had there been a Drivers' Championship in place at the time, he would have won three of them (his last in 1971) while driving Camaros in 1968 and 1969, and an AMC Javelin in 1971, all for Roger Penske Racing. During their enormous success in Trans-Am, Penske and Donohue would begin to experiment with their Camaros. They discovered that using a drag racing trick of dipping a car in an acid bath would eat away small amounts of metal, which in turn made the car incrementally lighter, and allowed it to be driven faster. The 1967 Z-28 won its last race by lapping the entire field of cars, causing suspicion throughout the paddock. During a post-race inspection, race stewards discovered that the car was 250 pounds lighter than the 2,800-pound minimum weight requirement. Donohue was about to have his race victory taken away for cheating, but Roger Penske stepped in. Penske warned that any disqualification would have the potential of motivating Chevrolet to pull all support for the Trans-Am series. After considering the potential consequences, the race stewards allowed Donohue's victory to stand, but the rules for the 1968 season incorporated a change whereby all cars would be weighed during the technical inspection before the race. Penske and Donohue did not stop acid-dipping after this, however. Continuing the practice of reducing weight allowed them to place weights of certain sizes strategically in specific locations within the car, thus helping to balance the car while being driven