Porsche Repair: 1984 928 Fuel, BTM motorwerks, regular vs premium fuel

Question
I read somewhere that with the 928's you have to use premium or supreme fuel, is this true or can you use regular? I've been using supreme and if you add regular to the tank that already has supreme will I have trouble.

Answer
Ifyou put regular in a tank of premium, it's not going to gum up anything like that. What your doing is lowering the octane rating. The engine was designed to run on 93 octane. If you put 89 octane in the engine, you will get pre-ignition or detonation which is very bad for the engine.