I now have a very nice Edelbrock 255 manifold.  My 55 Tbird is currently running with one Holley 465 4V.  I purchased a second 465 and am awaiting it's delivery.  Soon, I will be mocking up the dual quad setup.  This leads me into a few questions.

1. I can see the runners are a little smaller in the 255 than those in my "G" heads.  Will I need to port the 255 manifold or will it work as is for a street car?
2. Should I port the adapters?
3. Should I mount the carbs forward or backward?
4. I believe I will use direct linkage.  Is this best for a street car?

My 301 cu. in 292 is running perfectly.   It has a moderately bumpy cam and idles at 800 rpm.  The plugs are very clean with almost no discoloration.    The motor is nearly new and I am running a Pertronix unit and coil.  Do you think the second 4V will change my car's driveabilty?  I don't want problems.

Port matching at the intake ports going to the heads and where the carb adapters bolt to the carb flanges will be beneficial.  Some port work at the openings at the carb bores on the intake also helps.  The engine will run okay without doing this but will have better rpm capability when the ports are worked on some.
 
The throttle linkage is less complicated if the carbs are mounted forward.  There’s also more room (~½”) behind the carburetors if mounted forward.  If running the carbs so they are facing to the rear, then you’ll need a bellcrank for the throttle so the linkage can moved over to the right side of the engine.  If running both carburetors so the linkage is synchronized, then fuel distribution is expected to be the same regardless if the carbs are mounted facing forward or backwards.
 
For the secondaries to work as intended, the secondary diaphragm springs need to be replaced with either the long yellow or short yellow springs.  When using the carbs in pairs, the carburetor signal is reduced in half which essentially means that the secondary spring tension must also be reduced in half.  This is where the yellow springs come in.
 
As long as the carburetors are in good condition and jetted appropriately, the cylinders are expected to burn cleanly.  Idle fuel mixture is going to be important here as both carburetors need the idle mixture screws set the same. You’ll find that less idle mixture adjustment per carb is required when using them in pairs versus using just a single carb.
 
Here’s a picture of the FM255 with the Edelbrock #1106 carb adapters.  These will likely have the carbs too high on a Thunderbird engine but would work well on cars and pick ups where hood clearance is not as much an issue.
 

Lorena, Texas (South of Waco)

A$$uming the intake carb flange bores are 1.5" as is the ECZ-B 4V intake, I remember seeing a carb adapter that had throttle bores that were 1.5" on the base while a little larger on the carb mounting side (chamfer) that would allow a later larger throttle bore carb to be mounted without have to hog the original intake. This is for the small pattern mtg.

Anyone have reference to this adapter?

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Thanks for the information.  Can anyone tell me what these holes are for?  Can I mount a coil bracket in these holes?

Phil.  Below is an adapter available on the Speedway Motors site . . .

My copy-paste doesn't seem to work nor my importing of a Word document work-up.  Ugh!
Click the link below to see the Speedway Motors web site info.
https://www.speedwaymotors.com/Holley-Edelbrock-to-Carter-WCFB-4-Barrel-Carburetor-Adapter-Plate,5551.html




Hope this helps! 

NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Bore size is 1.5" on the small side and tapers to 1.685" on the large side.

Took care of the throttle bore size problem,

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Can anyone tell me what these holes are for?

Hot air choke heat source.

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https://www.holley.com/blog/post/4165_4175_carburetors/

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The 465 cfm carb is a 4160 style, not the ones in the above link.  You cannot install two 4165 style carbs on the Ed 255 manifold end to end.  Joe-JDC

JDC

The 465 cfm carb is a 4160 style, not the ones in the above link. 

... whoops ... mis-read ...

I thought the OP was stating carb style, not CFM rating.

THANX for catching that ...

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