Panic - I do not have one to look at, what size are the primary throttle bores/primary venturii on the Holley 390?

The small Carter AFB has a throttle bore of 1 7/16, and a primary venturi of 1 1/16 inches.

For comparison, the Pontiac Sprint Q-Jets (which are available) have the same 1 1/16 venturi, but the throttle bore is slightly smaller at 1 3/8 inches.

No argument, just would like to have the specs for all in the same spot.

You nailed the biggest issue with the Sprint carb, being the lack of an intake.

EDIT: for additional comparison, the primary venturi on the 265 CID Chevy WCFB is also 1 1/16 inch; while this was increase to 1 1/8 inch for the 283 CID Chevy.

Jon

Last edited by carbking; 03/10/2022 4:17 PM.
Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop