Hi all. I have a stock 57 Ford 312 engine bore .060 over when it was rebuilt and have been running a Holley list 1849 with mixed results.
I believe this is a 550 cfm carb. I experience idle issues, poor low end performance which leads me to believe that I might have
too much carb. Before I rebuild it, I am considering a brand new Holley 4160/ 0-8007 which is 390 cfm. Research shows that
list 1273 Holley came stock with the engine and was rated at 410 cfm. Engine is 322 cubic inches bored out and is stock in 
every other way (auto trans). The Holley carb selector points to the 390 carb to be the one to use. Any help that you can give
me to make a decision would be most helpful. I don't want to choose a carb that is too small either.

Scott

Redding, California

The Holley list #1848 4V carburetor is the recommended replacement for the 1957 Thunderbirds originally equipped with the Holley List #1273 carbs.  As such, the throttle linkage on the #1848 carb matches the original Holley.  Always keep in mind that the four barrel carburetors of the era were undersized on the various Ford applications.  Case in point are the 1957 E code engines which simply had two teapot carbs in lieu of the 400-410 cfm Ford, Carter, or Holley 4V carbs that were available on the single four barrel equipped 312’s.  With the 1957 312 single four and dual quad engines being the same other than the induction setup, the advertised HP rating was 25 HP higher with dual quads. Recent dyno testing has confirmed this to be the case and not just some marketing hype.
  
The old calculations for carb sizing work fine for stock engines that have little or no port work, small valves, and stock low lift camshafts.  Anytime the engine has been modified to improve the air flow in and out of it, then the carburetion should be examined to see if it will benefit by having it larger than what the old calculations suggest.  I’m currently running the Summit model 4010 500 cfm on my 272 which is basically stock other than having the Isky E4 camshaft and that carb is definitely undersized once the rpms are twisted up.  It’s a good driver though but if doing it again, I would opt for the Summit 600 or 750 sized carb on that same engine.  Keep in mind that vacuum secondary carbs are running on the primary side most of the time and if that primary side is sized smaller than a suitable two barrel carb for the same application, the carb is marginally on the small side.  I’ve installed a number of 750 cfm vacuum secondary carbs on hopped up Y engines and that is the carburetor of choice for both driving around and standing on the throttle.
 
Here’s the link to the article of a 303” Y build with unported heads and utilizing the Summit 750 cfm 4V  carb.
http://www.eatonbalancing.com/2015/05/01/unported-iron-heads-can-still-make-over-a-hp-to-the-cubic-inch/

Lorena, Texas (South of Waco)