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I'd think tightening would advance the timing. You can tighten it and if the idle rpms increase, you've likely increased the timing. Or you could call MSD and ask.
MSD says that 2.5 turns out is equivelent to factory opti, I read a post quite a while ago that said his would not run unless it was screwed in all the way. I just installed mine and started with it all the way in but the car surged at idle sometimes almost quiting. After messing with it and several trips up and down the road, I found it ran best with it turned two times out. I guess it depends on your cars set up or MSD has some quality control issues. Even the instructions dont specify. Good luck talking to MSD Tech. I had an unrelated question and I could have got a better response from my Dog!
When I called MSD it was two turns out for 0 advance.
Mine was 2 & 1/2 turns out when I got it.So I guess that anything between the two will work.The ECM will adjust it.
If anyone has better info let us know.
Keep waving,Ray