Rgalajda,
Here is another lesson. It is actually a good idea on older cars that had points ign & resistance wire [ or bal res ] to use a relay to power HEI. HEI is inductive ign. More voltage means more spark energy. Connecting one side of the relay contacts to the alt stud, battery [+] terminal or [+] terminal on the starter will ensure that the HEI gets max voltage; use a 10 amp inline fuse for protection.
My car, a GM car, originally had points ign. With the engine running, there was a voltage drop of 1v at the fuse box. Quite normal. So if I had fed my HEI from the FB, it would have been down 1v compared to the above procedure.
Mark.
Set the idle timing [ init +MVA ] that gives you the highest idle rpm. Forget about idle vacuum. Vac will be highest with highest rpm, they will coincide. The high[er] rpm is the engine making more HP from the timing, whatever that might be. Same deal with idle mixture setting. If you turn the screws & rpm increases, engine is making more HP & likes that setting.
6 Volts will NOT damage the coil.