The Porsches weren't winning when I saw the races. It was just at the tail end of the Nissan GTP winning streak and the beginning of Dan Gurney's Toyotas. The Toyotas were 4 cylinders, the Nissan V-6, Porsche Flat 6 and Mazda Rotary. Sprinkle ina few V-8s and I think Jaguar was running a 12.
At that time the IMSA cars were faster than CART or Formula 1. They all went broke though! They made a small fortune in racing so to speak.........