I know nothing, but from what I have been reading over the last five years, the straight leg boosters and the downleg boosters will have very different fuel curves. Annular boosters have yet a third.

Look at all the Holleys, the straight leg booster seems to be majority, but every now and then there's an application that calls for a downleg booster. Here's an example - The first 780 Holley that came on the 425hp 396 had downleg boosters. We'd call it a 3310. Then came the later iterations and boosters changed to straight leg once it became a "one size fits all" carb. Maybe BradH or someone else like Mark Whitener or Mr. X our resident carb rebuilder can explain some basics like what are the general characteristics of the three types of boosters. I'd prefer not to get into air bleeds, idle fuel restrictions, and such because it's hard enough to remember the characteristics of the boosters.

How about it, guys, I'm slowly learning the second layer of Holley carb knowledge.

R.