At the time of the 550 Spyder there were no turbos and no 3.6L flat six engines.
The RS designation refers to racing cars in Porsche lingo. However, all 550 Spyders were meant strictly for racing anyway. So there really is not much difference between the 550 RS and the "regular" Spyders.
When the 550 was built, it was initially called Porsche type 550, in accordance with the previous Porsche naming scheme. However, because the body type was a Spyder, it also became known as the Porsche 550 Spyder. In addition, its use in dedicated sportscar racing made it an RS.
Some Porsche 550 coupes (closed cockpit) were also built...
Porsche 550 RS Coupe, Pasha Inanov - LeMans is a very special type of race. Lasting 24hrs, the winning car is often the toughest, not the fastest. "To finish first, first you must finish", is the motto of... CG Cars Gallery