I am a new (again) Opel owner with a 71 Gt. I wish to do some racing with it as well as drive on the street. The type of racing would be closed course paved tracks as I am not interested in the rough and tumble motor cross stuff. My question is what can I do to the engine besides porting in order to increase torque and hp but still stay in whatever class needed in order to race "stock". IOW how large can the block be bored? Are you limited to .040 over or something? Or can you go to the 95mm size? effectively making it a 2.0? I will probably build up a 70 engine for racing as it already has higher compression and keep the 71 engine for street. I am just looking for advice in order to begin with the engine. Thanks for your help.