The Porsche 550 RS was the first Porsche which was specifically designed to be raced and was produced from 1953 to 1956. I came across two of the cars in July 1994 at the Coys International Historic Festival meeting at Silverstone. The first, and older car was amongst the group of cars destined for the auction which took place on the Saturday evening of the weekend-long event:
The second car was in the Porsche Owners Club area:
This Wikipedia article tells you about the car, and as it says it was a Porsche 550 RS which film star James Dean was driving when he had his fatal accident on 30th September 1955.