The SCCA (Sports Car Club of America) introduced the dual category system to Trans Am competition in 1977 and described the format as "two championships for the price of one". Many of the cars in Category I were from the SCCA amateur ranks, as B and C Production and A Sedan cars were eligible for the class. Most of these cars began as street vehicles that were modified for racing. The Category II cars were built strictly for racing. The class was for FIA Group 4 and 5 cars such as the Porsche 935 Turbo and U.S. GTs. The U.S. GT rules were quite liberal allowing builders to create tube frame chassis cars and almost any modification was allowed as long as the vehicle retained the original block and heads. As a point of comparison, a Category I Corvette with a 454 cubic inch engine was required to weigh 2,950 pounds and was restricted to 10-inch wide rims. This car would produce approximately 500-horsepower and the owner may have $20,000 to $40,000 invested in the car. It's Category II counterpart was allowed 16-inch wide wheels and if a 460 cubic inch engine was used the car would tip the scales at 2,500 pounds. A Category II Porsche 935 Turbo would produce approximately 700-horsepower and in 1979 would cost over $150,000. The photographs below clearly illustrate how different the same model of car could look when prepared to Category I or II regulations. But the dissimilarities under the bodywork are even greater.
As is the case with most professional race weekends, practice was scheduled for Friday and qualifying took place on Saturday with the main event going Sunday. Unfortunately, wet weather moved in Saturday morning and as often happens at Mosport the rain was accompanied by fog. Although a few cars made a brief appearance on the track in the morning the fog became so heavy that Corner Workers could not see between stations. The organizers decided to wait for an improvement in the weather but it did not cooperate enough to allow the cars to take to the track safely. The day's activities had to be cancelled and qualifying was rescheduled for Sunday at 10:00 am with the forty-lap race taking place at 3:00 pm.
When qualifying finally took place it was John Paul Sr. who captured the pole with a 1:22.583. After seven events Paul, the 1978 World Endurance Driving Champion, was the series points leader in his Porsche 935 Turbo. Almost half a second behind him was Ludwig Heimrath. Rounding out the top five qualifiers was the Chevrolet Monza of Tuck Thomas, Preston Henn in a 935 and Mo Carter. First in Category I and sixth overall was, the racing dentist, Frank Joyce in the Phantom Racing Corvette. Only two one-hundredths of a second behind was Bill Adam. Third in Category I was, the Placer County, California Sheriffs Inspector, Gene Bothello also driving a Corvette.
The period between qualifying and the start of the race provided some excitement for the local entries. Carter's Camaro was o