VintageMopar wrote:
The AFB had all 4 venturis like size of a quarter.
VintageMopar is correct. Carter AFBs have comparatively small secondaries, as well as Edelbrocks based on AFB design, molds, tooling, and so forth. (Edelbrock has evolved their designs, molds, and tooling over time so this is not true for
all Edelbrock carburetors.)
Comparatively small secondaries means less performance under load and WOT. I'm well aware I may find the AFB's performance lacking and may need to swap to a 1406, Quadrajet, or similar carburetor with larger secondaries.
Aside: Carter AFBs
figuratively suck because they
literally suck less (air) than other carburetors suck.
I'm not going to mention this to my daughter because she doesn't realize the beast she's putting together with her '59 Savoy project. I had a '66 Dodge Polara with a 383 which used to scream. (83 mph in 30 mph zone less than a half city block from a stoplight.). So, I'm going to covertly encourage her to stay with the AFB. (I can foresee her needing new rear tires within a few months ... I did with the '66 Polara.)
The Edelbrock 1406 has larger secondaries, although I don't know if they're as big as a Quadrajet or Thermoquad.
Your Thermoquad is a spread bore (larger secondaries) so the intake manifold
should also be a spread bore. Assuming the Thermoquad is OEM stock ... a previous owner may have replaced an AFB with the Thermoquad. In that case, your intake would be a square bore.
One way to tell is take off the air cleaner, open the secondaries butterfly valve, and look for a 'step' between the carburetor and intake manifold. Do this now because if you have a square bore intake, it's gonna throw a wrinkle in everything we've been talking about.
(A spread bore carburetor on a square bore intake manifold -- or vice versa -- means less than optimum performance.)
Here's a good article to read on carburetors. Bear in mind the article is listing likely mistakes rather than making recommendations.
