hi
Can someone explain to me how many degrees I can move to compensate the reduction of compression ?

example at 15psi 10:5:1 i use 15ēdegrees advance
at 15 psi 8:5:1 i can use ?

 

I still wouldn't know the answer, but what is the change in your dynamic compression? Wouldn't that be more relevant?

 

the question is! if i reduce the compression of engine i can use more ignition advance? if i can ! how much more?

 

Can you use more advance? Almost certainly. How much? I don't think you've provided enough info to answer that question. What is your engine setup, particularly your cams? What is the flow rate of your turbo? Even with this information I'm not sure anyone could give you an exact number. The best thing to do would be to make small increases in advance until your plugs show any sign of knock, then back off a few degrees. Correct me if I'm wrong.