I have always understood it this way. Annular boosters react sooner and quicker to vacuum than downleg boosters. Annular boosters work better on heavier cars and help with low RPM performance. Of course it is more complicated than that, but that's sort of the "Cliff Notes" version.
Crew Chief "Tip of the day":
Most handling problems can be solved by adjusting the screw-ball. It can be difficult to fine tune at times. Explaining yourself loudly and striking it on top of the helmet with a dead blow hammer usually works well.
Bookmarks