performance curve distributor
depending on how radical a build is, you may see very little change in fuel economy without vacuum.
Vacuum advance sure comes up for debate a lot.
BUT that is a different topic...
Curve can make a big difference.
This year I shortened my curve to 12 degrees (was 16). Bumped initial from 20 to 24. Picked up 2 tenths. It surprised the heck out of me.