Still working on trying to figure this out and I think I am coming around.
The VE table = calculations or a assumption of how efficent the motor is at a given cell on the map in relation to kpa's and engine speed (rpm's).
When you upgrade your heads, intake, throttle body and etc.... theorectically you are now getting more air in the motor.
If your stock setup is more restricted than your new setup, and your ve table is still based on the old setup, why or where is the computer getting the idea to add more fuel, if it is reading off the old un-edit ve for the more restricted combo?

I am determined to figure this out.

 

Don't quote me but I would think the MAF is reading more air coming into the motor and adjusting fuel. The MAP sensor also helps in that; as well as the O2 sensors. I could be wrong just my $.02.

 

computer looks up whatever values it's got--if it's untuned, it's gonna pull wrong values and make wrong decisions based on it, resulting in rich or lean condition. that's when trims kick in, and computer approximates how much less/more fuel to dump depending on the trims. also, trims are used to alter the VE, if a cell gets repeatiedly rich trims, then the cell will be made numerically smaller, so the computer sprays in less fuel next time around.

tuning is nothing but speeding up and forcing the learning process (some areas are unlearnable, since trims are off in Open Loop). precision is usually improved by disabling many modifiers influencing airflow measurement or spark, allowing more consistent burn.

 

Closed loop fueling

 

Thanks Red Hard! That help alot.