After Group B rally racing collapsed in 1986 due to a spate of fatalities, Audi sought new a motorsport venue for its game-changing Quattro 4-wheel-drive system. After a brief stint in the American Trans-Am series, Audi set its sites on the 1989 IMSA Camel GT championship, specifically the GTO class ("O" for GT cars over 2.5 liters).
They lifted the engine and drivetrain from the 2-door Group B rally car and dropped it into a tube-frame racing car, built to resemble the 4-door Audi 90. According to the homologation rules, the only piece of the original Audi 90 that had to be utilized was the roof.
The result was an impossibly wide, 720 hp track beast that dominated the 1989 season. By spreading the acceleration loads over all four wheels, the Audi made better use of its power with less tire wear. The car could brake later, corner faster, and take virtually any racing line.
Despite dominating the field, Audi didn't have the car finished in time for the first two races of the season and thus missed an opportunity to contest the championship. Still, proved to be a major technical and performance achievement and today is seen as a legend.