In testing, it soon appeared that the Porsche 917 did not work well on the race track. Brian Redman recalls that “it was incredibly unstable, using all the road at speed.” Many thought that the 4.5 litre engine was too much for the frame. The suspension and the stability of the frame were suspected, but modifications did not improve the problem. It was finally determined that the “long tail” body was generating significant lift on the straights, as the 917 was 30 km/h (19 mph) faster than anything previously built for Le Mans. As with former underpowered Porsches, the 917 aerodynamics had been optimized for low drag in order to do well on the fast straights of Le Mans, Spa, Monza and elsewhere. The significance of downforce for racing was not yet fully realized even though Can-Am and F1 cars were using wings by that time.

Before its competition debut on 11 May 1969 in the 1000km Spa, the weather conditions prevented further improvements in tests. Jo Siffert/Redman managed to clock an unofficial lap time of 3:41.9 which would have beaten the pole of 3:42.5 set by a Lola, but they chose to use the 908LH long tail with which they won the race and set the fastest lap at 3:37.1. Gerhard Mitter/Udo Schütz actually started the race from 8th, but their already ailing engine failed after one lap.

Three weeks later for the 1000km Nürburgring, all works drivers preferred the 908 over the 917 which was, despite some modifications, not suited for the twisty track. As it was necessary to promote the car in order to sell the surplus ones, Porsche asked BMW for the services of their factory drivers Hubert Hahne and Dieter Quester. They practised, but Munich declined permission to have them race, so Englishman David Piper and Australian Frank Gardner were hired on short terms. They drove the 917 to an eighth place finish behind a Ford and an Alfa, while the factory’s armada of six 908/02 spyders scored a 1-2-3-4-5 win after the only serious competition, a sole Ferrari 312P, failed.

At the 1969 24 Hours of Le Mans, the 917s were quickest in practice. Soon after the start the poor handling of the 917 and the inexperience of one of the drivers resulted in drama: British gentleman-driver John Woolfe crashed his Porsche 917 at Maison Blanche on lap 1, dying as a result. Woolfe was the first privateer to race a 917. The works 917s led the race for hours, but did not make it through the night. At the end, Hans Herrmann’s 908 remained as the only Porsche that could challenge for the win, but Jacky Ickx’s more powerful Ford won once again, by a mere 120 metres (390 ft).

During June 1969, Enzo Ferrari had sold half of his stock to FIAT, and used some of that money to build 25 cars powered by a 5 litre V12 in order to compete with the Porsche 917: the Ferrari 512 would be introduced for the 1970 season.

At that time, the 917 already had several races under its belt, yet no success. The first win came in the last race of the championship season, the 500 km Zeltweg. Jo Siffert and Kurt Ahrens succeeded in the privately entered Porsche 917 of German Freiherr von Wendt. At that time, the factory had started to focus on development, leaving the time-consuming trips to races to customer teams.