I swapped out my MSD dizzy with no vacuum advance for a Ford upgraded with a Pertronix with both mechanical and vacuum. What a difference. A non vac. advance dizzy is great for drag racing where 95% of the time you are a WOT. How many of us drive our car like that? Vacuum advance with mechanical advance permit these engines to perform as the engineers designed them to. What I have experienced is, smoother transition from idle to hard acceleration, quieter note an idle with the indisputable roar of a BB when the pedal is down, cooler temps and no fuel noted in the
oil analysis from running retarded timing. Every
oil analysis until I made the change showed a significant and troubling fuel contaminate in the
oil. Talk to a powertrain engineer and ask them if vacuum advance is important on a high performance street engine and you will get the same answer every time. Just my 2 cents. Rick 428 FE