The Pikes Peak victories whetted the company’s appetite. In 1988 Audi took part for a year in the American TransAm race series. The engine installed in the Audi 200 quattro was the turbocharged five-cylinder unit that previously powered the world rally championship cars, in the meantime developing 375 kW (510 bhp), enough to secure the title for the American driver Hurley Haywood. Audi in fact took the chequered flag eight times, a total which secured the manufacturers’ title as well.
A year later the company switched to the IMSA GTO series, with its less strict rules. Only the silhouette of the Audi 90 quattro was retained: under the GTO’s carbon-fibre skin was a pure racing car. The five-cylinder engine, in its final development stage, produced 529 kW (720 bhp), and the car’s four driven wheels had 14-inch wide rims. With seven wins in 13 races, Hans Joachim Stuck took third place in the championship and the team came second in the manufacturers’ rankings.
In 1990 and 1991 Audi entered its flagship model, the V8 quattro, for the German Touring Car Championship. The 3.6-litre engine of this luxury saloon developed 340 kW (462 bhp). Despite the car’s basic weight of 1,220 kilograms, this was sufficient in conjunction with the car’s all-wheel drive to hold off less powerful but lighter rivals. Stuck took the championship title in the first of these two seasons; in 1991 the young Frank Biela pipped him to the post after a dramatic neck-and-neck finale on the Hockenheim Ring circuit. In 1992, when the season had already started, a dispute arose regarding the legality of the engine’s new crankshaft, whereupon the team withdrew the V8 quattro from the remaining races.
Audi’s most successful season in touring car racing was 1996. The A4 quattro Supertouring, with a power output of 221 kW (300 bhp) from its two-litre, four-cylinder engine, was entered for seven national championships – in Germany, Great Britain, Italy, Spain, Belgium, South Africa and Australia – and won them all! In the German Super Touring Car series the winning driver was Emanuele Pirro; in Great Britain the victor was Frank Biela.