Keep in mind also that the vacuum advance was used for spark retard under load when accelerating (not for gas mileage as some think) because the vacuum advance was hooked up to a manifold vacuum source (one that exists only at steady state rpms) and so would disappear on acceleration from any rpm. When the aviation industry started using auto engines, they wanted to use aviation carbs, and those carbs don't have vacuum advance mechanisms. Instead, they just use mechanical advance, and set them for total mechanical advance MINUS THE VACUUM ADVANCE IN THE TOTAL NUMBER. You DO NOT WANT TO USE THE TOTAL ADVANCE MECHANICALLY THAT WAS USED WITH A VACUUM ADVANCE. This cannot be done safely with fuels available today. YOU WILL DETONATE EVEN IF YOU DON'T HEAR IT! I have worked on hundreds of cars that had knock sensors on them, and have seen the sensor going off due to detonation, and never hear a ping or knock. With open exhausts typical of aviation engines it is even harder to hear it. That is why the TOTAL ADVANCE NUMBERS ON THE VW ARE 25 TO 28 (add 8 to 10 degrees for vacuum advance).
Bottom line is that if you want more from your VW or Corvair than base plus mechanical, add a carb or fuel injection that offers vacuum advance, and add a vacuum advance distributor. If you are compelled to have separate ignition systems, get the universal MSD crank trigger system and MSD box for complete redundancy. I published the numbers a while back for the parts needed. Colin Rainey brokerpi...@bellsouth.net
