Forced induction opens a whole nother can of worms. Having some vacuum advance might help a bit (as outlined above), but you want it active only when the intake manifold (engine side of the blower) is still below atmospheric pressure. The problem with tapping under the carb is that it might still have vacuum when the blower is pressurizing the manifold.
But the real kicker is that the spark needs to be retarded when running under boost and when the charge gets hot (from being compressed by the blower). You're probably a lot better off running some sort of computerized timing control, that can monitor both manifold pressure and temperature to optimize timing.
56 TR3 TS13571L daily driver
71 Stag LE1473L awaiting engine rebuild
7? Stag awaiting gearbox rebuild
Having trouble posting or changing forum settings?
Read the Forum Help (FAQ) or contact the webmaster