[vector1]

mechanical and vacuum are two independent type advance mechanisms. the mechanical will always be there, from 10*-32* for example as the rpms increase, usually all in around 2500-3000 depending on engine, and can be considered base advance. the vacuum will be on top of this. when you light cruise down the highway the high vacuum is going to advance the "base" timing which helps mpg, my crate engine sees close to 50* advance. but when you open the throttle the vacuum drops and vacuum advance will drop also so you don't ping on acceleration, but never less then the mechanical. i have read some don't like the vacuum advance for racing as it will not react quick enough to retard the timing on acceleration. vacuum advance can be tuned also as you have noticed along with different tension springs i believe. some vacuum setups will also retard the timing, ala oem.