The FIA's Group 5 started out in 1966 with the introduction of the "special touring cars" class. Its fourth and final evolution came a decade later, and the new "special production cars" designation meant that, for 1976, teams could do extensive modifications to their production-based vehicles.
BMW introduced its replacement for the outdated 3.0 CSL in 1977, after what became known later as "the Flying Brick" was developed in just over 12 weeks. Basically, the masters at BMW Motorsport jammed their 300--horsepower Formula 2 engine into the wildly widened body of a 320, because that was okay to do back then.
Doing high-speed demonstration laps around the wet and half-frozen Goodwood circuit with such a car is certainly challenging, but the 320 Turbo had bigger worries in period thanks to a fleet of extreme competitors based on Porsche, Fiat, Ferrari, Toyota, Nissan, Mazda, Lancia, Ford, Lotus, and even Corvette production models.
Despite all that, the Group 5 BMW 320 Turbo remained competitive well into the 1980s.
And if you're wondering how the rest of the Group 5 field help up against the punishing weather at Goodwood, please enjoy the following 40 minutes: