The GTS and GTS Club Sport variants of this fascinating ‘transaxle-era’ Porsche are perfect examples of how a group of dedicated racing engineers can turn a mild-mannered GT coupé into a very muscular automobile.

The 924, introduced to replace the 914 as Porsche’s entry-level sports car, struggled initially.

Its Audi-derived two-litre inline-four was underwhelming in the power department, despite its exemplary road manners thanks to a 50/50 weight balance.

Sales were initially disappointing, and Porsche decided to add some badly needed muscle, beginning with the 924 Turbo.

From there, Porsche’s racing department began to develop a package of semi- and full-competition parts that would boost the model’s pedigree.

The Group 4 Type 937 GTS was the next step upward; 50 were constructed of which just 15 – all painted Guards Red in left-hand drive – were built to ‘Club Sport’ specification.

The GTS and Club Sport were similar in appearance, with fiberglass-reinforced polyurethane front...