[vettestr]

The decision to run or not run vac. advance on my/your engine should be a tempered choice. A complete performance tune needs to look at the pros and cons of the overall system with intended goals in mind.


I do think there are some benefits to VA (vac. advance) but the higher the modifications from stock the lower the VA benefits. In every case VA must compliment not complicate the performance of the total system. VA has multiple components that need to work well before we even discuss when and how advancing ignition timing is beneficial. I like electronic timing Maps or controls but mechanical .... not so much.



The items that allow vacuum advance include A> a rotating plate, B> an arm to mechanical move this plate, C> a vac. diaphragm housed in a canister, D> then a source for the controlling vac. In the old days the ignition points (1 or 2 sets) lived on this rotating plate and was a source for timing error and so on. In short each component and its movement/function can be eliminated without having VA on your engine. If present you must verify they each work without inducing other problems. To be sure you can argue mechanical Vacuum Advance aids in emissions reduction and can increase fuel mileage under certain conditions. Greenies may hate me but MY Engine was not built with emissions or fuel mileage in mind. I control ignition timing through my fuel injection controller and have a solid mounted pickup plate in the distributor for these reasons.

My opinion only..... mechanical vacuum advance is more trouble than value the way most folks bring me the car. I find less trouble when MSD with general spring changes were installed but they still need a lot of tweaking.