ok,on this subject consider me totally ignorant...
-your base timing is what you set your distributer to.
-your total timing is your base plus what your prom tells it to add.

What if your cam is advanced....

just trying to get this straight...

 

Timing is related to ignition only. You reference the ignition timing to crank angle, so cam advance does not figure in.

However, advancing your cam will change your power band.

 

Base timing is the timing at the distributer when the ESC (electronic spark control) is disabled. What this means is that the timing will not advance or retard due to the ESC (or ECM).

The total timing can be a little confusing. Not so long ago.. when all you had was vacuum or mechanical advance controlling your timing, all you had was a pretty linear spark curve from your "initial" timing (at idle) to your "total" timing (which would usually be something like 30-32*). You could change springs to control the total timing and also when (at what rpm) this total timing came in at.

With the advent of Electronic Spark Control this all changed. Now you have complete timing control at any given rpm and load. So you can have an initial timing of say 12* at idle, then advance the timing to something like 38* during normal cruising loads (for better automization and gas mileage), and then bring the timing back to 30-32* at WOT (too much advance here will cause detonation).

Even with the Electronic Spark Control when people talk about "total" timing, they are still refering your max. advance at WOT (like the "old" days).

I hope this helps to clear up your question...