Damen,
I think Enrico Walcher was teammate to Andy Bovensiepen in the Porsche Zentrum Bielefeld team. Maybe Armin Knüpfing ran that car, I don´t remember. He started to have his own team those days, but not yet in the Carrera Cup, if memory serves correctly.
Team Porsche Zentrum Bielefeld was run by a strange guy called Knut Mentel, a buddy of Roland Kussmaul. At least two mechanics of 1991 are still working at the Porsche Zentrum Bielefeld. Innocent days, the teams used to come with a van and a trailer for the race car, no trucks, no hospitality. Things changed very quickly then.
Maybe there´s some stuff left in PZ Bielefeld´s archives.... the guy running it today is Mr. Frank Menzel, nice man and sponsor of Konrad Motorsport today. Phone +49 (0)521 41 00 64. As the owner of the former race car you´ll get infos, in case they have anything. Let me know, if you want me to support you.
Hacki