GTlover:

However, the fact that the new racing engine is not in the RSR is a "disillusion for me"...I expected this to happen...but I still dont get it what Porsche is doing there..

Maybe it is very simple... engineering ressources. I doubt that any serious racer at Porsche would want to use the old engine if they could employ the new one which comes with some serious advantages (weight savings, fuel efficiency).