Mike, I was running a strict mechanical MSD dizzy on my 428 single carb FE. After an evaluation from a number of my GM power train engineer friends, they all agreed that unless I was running at WOT all the time a vacuum advance dizzy was the way to go. With out vacuum advance at partial throttle, where we operate 98% of the time, we run a retarded timing with the associated wear and poor fuel combustion. I made the switch to a Ford distributor with a Pertronix module and vacuum advance. Much better drivability and with the throttle wide open, it has the same curve as the MSD. I set up the distributor for 36 degrees BDC at max mechanical advance. The vacuum provides and additional 16 degrees at partial throttle. Hook up to a ported vacuum (Off the Carb),not manifold vacuum. The engineers that set up these high performance FE's in the day had a lot of engineering behind them. If straight mechanical advance was better and cheeper they would have used it. This was before anyone was concerned with mileage. My change yielded a better idle, quicker throttle response, quieter exhaust and a cooler running engine. No down side. Rick
