GT-Cars are low-volume-produced cars (at least 400 built in 24 months) with at least two seats, which resemble as far as their look is concerned, largely the road-version. They may be improved with the aim in mind to make them more suitable for racing. Modifications must be according to the international motorsport-regulation scheme.
The race-versions were shipped to the tuner in their very early stages of completion by ItalDesign. In total there were 54 frames built up as race-versions. Schnitzer and Heidegger received 4 of them. The remaining ones went to the Motorsport GmbH (Germany), Osella (Italy) and Ron Dennis (Great-Britain). Beside development, test and release of modifications for the tuners, the Motorsport GmbH also prepared the 5 racing-versions provided for the Formula 1 pilots for each race.
The Group 4 M1 had a weight of 1020 kg ready for race. Therefore it was on the safe side concerning minimum weight by 50 kg. For the Procar races it did not make a difference, but not when it came to racing against Porsche and Ford. The BMW M1 had the reputation of being nasty due to its very small safety margin. Furthermore braking was quite a challenge due to its considerable weight.
Marc Surer could lap the old Nürburgring in 7:55,9 minutes in his Group 4 M1.