In 50+ years I'd seen precisely one 904 / GTS, if it wasn't a fake, and after 10 minutes in the paddock, here were TWO, and a third appeared not much later!

Most people call the GTS coupes "Porsche 904", which they might have started as... They were intended to get the 901 (we know it as 911) 6 cylinder motor and if they had, all, gotten the 901 motor, we'd all call them 904s and that would be the end of it.

But the 901 motor wasn't ready when the 904 chassis was ready to go as a customer racing car... so all the production coupes had the Carrera 4 4-cam, 4 cylinder engine. People had paid money and expected racing cars, and so 100+ (some say 120) were assembled and most were sold. One was dropped vertically (nose first) to simulate a front-end collision- a USA requirement I believe.

When the 2.0l 901 six was finally released for production, it was a brand new design making baby steps, with a single overhead cam for each bank of cylinders, whereas the Carerra 4 was a known and fully developed giant killer. The shaft-driven cams were a mechanical masterpiece or nightmare, depending on your prejudices, but it was light and powerful. The factory DID put the six into some 904s and muddied the water by calling them "906s". When they started working on the new engine, it was soon making good horsepower, and promising even more than that. Oops. Suddenly, the 904 buyer who had accepted a Carrera GTS had an obsolete racing car that was less than 18 months old. The 901 motor would have fit just fine, but the cost of a retrofit wasn't in the cards. There had been enough customer interest to see a second set of wheels, hubs and suspension pieces ordered for a second batch of GTSs, but besides the engine issues, it was now clear that the machine-sprayed fiberglass bodies, made by Dornier Aerospace, were inconsistent in weight and strength. (The same issue just about killed Lotus's contemporary coupe - which is why the Elan roadster got a "backbone" steel frame that the drive train and all 4 wheels were attached to...) Worse, even perfect bodies, bonded directly to the stamped steel rail frame, made the frame un-inspectable corrosion bait. It was time to retrench.

Family member Ferdinand Peitch (one of Ferry's nephews, a son of his sister), now head of VW, was put in charge of the racing / engineering effort and he cancelled the Carerra GTS second series. A new car, which we usually call a 906, was quickly schemed around the 901 six cyilinder motor and the Carrera GTS wheels and suspension parts now arriving. Peitch walked back Porsche's racing car technology to the tried and proven tube frame with unstressed bodies. Fiberglass bodies, removable so that the frame could be inspected. Well... he then decreed that Porsche would build new cars for each significant race, and sell them to customers after the race. As used racing cars, utility and maintenance issues were more clearly the owners problems, but the customer got the latest and greatest technology, no lag between factory and private owners.

All of this messed-up the name of these cars AND the "Carrera 6" which is usually (but incorrectly) called "906". , all the production "Carrera 6s" had the 6 cylinder 901 motor, but the factory raced GTS's with the six and the Carrera 6s with the 8 cylinder from the F2/F1 car.... Growing pains.

Very few people remember today that the 912 (nee 902) with the 4 cylinder, pushrod, Super 90 motor, outsold the 911 (nee 901) 2:1 in the first year they were available. 912s would be discontinued when the VW-Porsche 914 entered production. It was available with a VW-based 4 or a Porsche 901 6... and there were half-year 912E's (with the VW-based, Porsche-headed 914 4) between the 914 and 924... more growing pain.