The M3 may have shared a passing resemblance to the garden-variety E30-generation 3 Series when it broke cover at the Frankfurt Motor Show in 1985, but beneath those boxy rear arches lay wholesale mechanical changes introduced to homologate the model for Group A Touring Car competition.

Advanced features include independent front and rear suspension with gas dampers, an anti-roll bar, and servo-assisted ventilated disc brakes—not to mention a wider track with beefed-up wheels and tires.

Most notable, however, is the Paul Rosche-designed “S14” engine—a 197-horsepower, 2.3-liter double-overhead-cam four-cylinder which made the M3 an overnight performance legend.

In its inaugural year of availability, privately run and works-backed M3 entries dominated the World, Italian, Japanese, and German Touring Car Championships.

The model continued this success streak with further titles in the 1988 European Touring Car and 1989 German Touring Car series, two British Touring Car crowns (1988, 1...