Without using this new method the MSD computer would try to start the car at 18' timing (thats 38 locked minus the 20' retard it creates). The 18' is too much sometimes and sometimes causes a hard start. The engine is 9.7:1 compression, 93 octane gas, and the somewhat radical cam. So 18' is not really an ideal timing to crank the engine when its all hot and warmed up.
With using the vac advance now, my timing on start is close to ZERO before TDC. Since the vac advance is "off", my dizzy is locked somewhere at like 18' TOTAL now (no longer up at 38') and the MSD computer will retard from that new setting of 18'. The computer says "upto 20' retard" so Im sure its close to 0' on cranking.
See my point? My dizzy is now locked at maybe 18' instead of 38' total advance.
Its like turning my dizzy before I crank the car, then advancing the dissy once its started. The vac advance is doing that for me