In 1967 Porsche prepared a small number of 934 Porsches with 935 Group 5 parts for the Trans-Am and IMSA GTO series. In the end, the 934/5 dominated the Trans-Am series by taking to top five positions in the championship. Ludwig Heimrath became the 1977 Trans-Am champion in his 934/5 by protesting Peter Gregg's highly modified car. Together they humbled the Corvette C3s and the Group 44 Jaguar XJS.
Using the 930 Turbo as a basis, Porsche built the 934 for Group 4 GT racing. It replaced the outgoing Carrera RSR while winning GT Championships in Europe and performing very well in America for Trans Am. Porsche built the 934 from a standard 930 bodyshell and production rear spoiler, but almost nothing else was left alone. The suspension was converted to solid mounts and nylon bushings with adjustable anti-roll bars.