|In 1973, the International Race of Champions (IROC) league was formed. The top drivers from other leagues, such as IRL and NASCAR, were invited to prove their abilities against each other using identically prepared vehicles selected by the league. During the first year, the Porsche Carrera RSR was used. The first IROC I race was at Riverside International Raceway in California on October 27, 1973. The race was 76.2 miles long with the average speed being 101 MPH. The famous Mark Donohue led all 30 laps and took the checkered flag. Mark went on to win three of the four races during the first year of IROC racing.|
Due to the high costs associated with building and maintaining the Porsche's, the Chevrolet Camaro was used during the second season and continued through 1980 when the league decided to take a break. In 1984, the league returned and once again featured the Chevrolet Camaro. In 1989, due to high costs associated with sponsoring the event, Chevrolet decided not to renew their contract with IROC. This meant that their IROC series of Camaro's were unable to be produced anymore.
As of January 1, 1990 at 12:00 AM, Chevrolet could not longer sell the IROC-Z.
The $659 IROC-Z option was available on the production Camaro Z28 from 1985 through 1987. In 1988, the Z/28 was no longer produced and the IROC became an independent model. The IROC option featured mechanical and aesthetic enhancements which improved the performance and handling of the vehicle and made the vehicle more visually stimulating. The package included 16 inch aluminum wheels with P245/50VR16 Goodyear Gatorback tires. The front and rear suspension was improved by adding rear Bilstein gas shocks, Delco front struts, and larger stabilizer bars. Due to the tires and suspension, the height of the vehicle was lowered.
Originally, the engine selected was the L69 which produced 190 horsepower. Also available was the LB9 which featured 215 horsepower but was only fitted with a four-speed automatic. In 1986 through 1989, Chevrolet used the LB9 engine which was now rated at 190 horsepower but featured 295 ft-lbs of torque. By using electronic port fuel injection and mass air flow sensors, the greater torque rating and better fuel economy was achieved. In 1989, the horsepower was increased to 230 in the LB9 engine. The torque rose to 345 ft-lbs.
In 1990, a driver side airbag was added which greatly improved the safety of the vehicle. The instrument cluster was updated. The TPI system was changed from the Mass airflow system to the Speed density system. This improved the horsepower rating by five.
The horsepower rating was nothing like the 1960's and 1970's which saw vehicles produced with ratings of 400 and 500 horsepower. This was due to a number of reasons. Government safety and emission regulations, insurance costs, and fuel economy were all major ingredients in dictating the size and efficiency of the engines and the vehicle. All manufacturers were forced to abide by guidelines which focused on safety and fuel economy and took away horsepower and performance.
In 1987, the mechanical and aesthetics of the vehicle were once again improved. The L98 engine became available as optional equipment. This was the same engine used in the Corvette and produced 224 horsepower, however, could only be acquired with an automatic, four-speed transmission. The front of the vehicle was altered; ground effects adorned the bottom of the vehicle. To make the vehicle more noticeable while driving down the streets, Chevrolet offered new, brighter colors.
Also in 1987, a convertible option became available at a cost of $4500.
When Chevrolet decided not to continue its support for the IROC league, Dodge stepped in and offered their Daytona.
The 1975 IROC season opened at the Michigan International Speedway in Brookly, MI on September 14, 1974. This was the first of four races and the first year the Chevrolet Camaros were used. The race was 100 miles long, consisting of 50 laps on the 2 mile oval track. Bobby Unser was the winner of the 1975 season, winning two of the four races. The other two races he finished second and third.
In 1976, A.J. Foyt won his first IROC title by earning the most amount of points during the four races. He did not finish first in any of the races. This was true for the 1977 season as well. A.J. Foyt was the victor without winning a single race, just by accumulating the most points throughout the season.
In 1990, the Dodge Daytona vehicles were now being used. Dale Earnhardt not only won the first race, he became the IROC champion in 1990.
In 1994, the Dodge Avenger replaced the Daytona. The Avenger was used until 1996 when it was replaced with the Pontiac Firebird Trans Am.