So I have a rebuilt 4100 (65 1.12 model) on the car now. I just bought a Holly 1273 (needs total rebuild). I got the holly as a spare and was just curious about how the two carbs would perform. So I have a few questions:

1) How well do you think they will perform against each other? Pros/cons/power/mpg etc.

2) I have two adapter plates for a pcv valve. One is 1” and the other 1/2” both with openings at the back for the hose from the pcv valve. Which one is better? I will post pics of the bottom where the ‘grooves’ are tomorrow.

Thanks,

Mike

Y’s like carb spacers so go as tall as you can.  The four hole spacers help the low end torque numbers versus the open spacers.  Be sure that the holes in the intake manifold match both the carburetor spacer and throttle bores of the carburetor.

Assuming both carburetors are rebuilt back to stock specifications, you will find that the 1.12” venturi Ford carburetor will outperform the Holley List #1273 carb.  This is based on the 1.12” Ford carb simply being a larger sized carburetor than the List #1273 Holley carb.  The Ford 1.12” carb is typically rated at 520 cfm while the Holley 1273 carb is in the 400 cfm range.  The annular discharge nozzles on the Ford carb are also a superior design when compared to the straight leg fuel nozzles on the Holley carb.  The annular discharge nozzles do a better job of atomizing the fuel as it enters the air stream and subsequently provides better fuel economy.  Here’s the link to some serious carb testing that was performed on a 312 with a ECZ-B iron intake.  Sometimes it’s not necessarily about the size of the carburetor but how well it meters the fuel into the engine.

Four Barrel Carburetor Testing on The Y – Eaton Balancing

Other opinions always welcome so chime in.

Lorena, Texas (South of Waco)

Thanks Ted,

It looks like, according to your test runs, they should be about equal in power/torque. Although I am curious why the race prepped Ford did poorer than the other carbs? was it just over carb that particular engine? Tim built my engine with a slightly warmed over cam just to help her breathe a bit better.

Mike