S135 (f suffix for X19) doesn't come with a vacuum advance, and early US models had a Ducellier distributor with a vacuum retard mechanism.
If you want Marelli PLEX style electronic ignition for a SOHC with vacuum advance there are plenty of those, lots of Ritmo / Uno / Regata in the UK.
Most performance cars don't worry too much about static advance, they are more concerned about maximum advance at revs, Alfa Romeos for example (but older Ferrari and Lambo are the same) have two marks on the crank pulley, a P and an M
P is Piano (slow in Italian) and you set the idle ignition timing at that mark, but the more important check is the M - Massimo (Maximum) and you hold the engine at 4000rpm and adjust the distributor so the crank pulley mark lines up with the notch in the timing case.
Everything changed when lead went out of the fuel though... leaded fuel burns slower than unleaded (avgas despite being high octane burns slower again) so requires a different amount of ignition advance to combust the fuel / air mixture so as to gain maximum power / efficiency while the piston is still up towards the top of the bore and cylinder pressure is high, if the fuel burns slower and the initial ignition advance (BTDC) isn't sufficient then a lot of energy is wasted due to the piston being too far down the bore to exert full force when the fuel is fully ignited.
The popular belief is that knocking / pinging / detonation occurs when the piston is at or before TDC is a myth, it actually occurs when the piston is around about 2.5 / 3mm or so down the bore on the power stroke, as it's about this point when any unburnt fuel air mix has enough volume and has sufficient space between the piston and head so there is negligible quench effect, the fuel air mix is hotter and can self ignite.
SteveC
