Vacuum secondaries are very forgiving in that the secondaries open up only as much as required.  That’s assuming that the original design was not tinkered with after the fact.  When doing the Holley carbs in dual applications, the vacuum signal is essentially reduced in half to each carb which requires a ‘half’ tension secondary vacuum spring so that the secondaries still open at a reasonable rpm rather than a very high rpm or not at all.  The long yellow spring in the secondary spring kit is a good starting point.
 
Drivabilty all hinges on how the carburetors are set up.  Assuming the linkage is smooth and the carburetors are properly adjusted, then should be fun to drive.
 
Linkages for such setups usually have to be hand fabricated.  There are some linkage kits available for the crossways mounted carbs on tunnel rams and those kits can likely be used as the basis with some modifications for hand built dual quad setups.  Here are pictures of the linkage on my EMC engine entry which started out as a tunnel ram linkage kit.
 

 

Lorena, Texas (South of Waco)

Thanks Ted.  Those are great photos.  Where can I buy linkage like that?  Can you please comment on the drive ability of this setup? I realize that is a lot of CFM for a 292.  I doubt my secondaries will ever open.

That top picture was one of my builds.  That intake manifold is the Edelbrock FM255 which has a wider carburetor spacing than the Edelbrock 257.  That wider spacing allows the use of inline model 4160 Holleys without a specialized offset carb adapter.  Many of the dual quad manifolds for the Y can facilitate mounting the carburetors sideways and not inhibit air flow to the banks due to the staggered inlet pattern within the plenums.  Here are pictures of the sideways mounted carbs on a Y in a station wagon.

 

 

Lorena, Texas (South of Waco)

Here are two photos of a Y Block with Holley carbs mounted in line.  How is this done?

At least some of the 2x4 intakes can have the carbs mounted sideways and still function as dual plane because the planes criss cross each other, rather than parallel like a single carb intake.  Is the Edelbrock not one of them?


Lawrenceville, GA

Y Block intakes are dual plane, and need the carbs mounted front to back, not sideways.  Your primaries would both be on one side.  Edelbrocks, teapots, will work and look great.  I have Edelbrocks on my 257, and if I remember correctly Vic C races Edelbrocks on a 257.  Joe-JDC

JDC

I don't think modern Holleys will fit without either custom adapters or mounting them sideways, which complicates linkage.


Lawrenceville, GA

I have located an Edelbrock 257 Manifold in NOS condition. The price seems reasonable, so I am going to pull the trigger.  I am now contemplating the carbs.  I can buy some old carbs and deal with those issues, or find some new carbs that will work on my Y Block.  Edelbrock 500 cfm Thunder Series AVS carburetors are one option.  I already have a new Holley 0-1846-1 465 cfm carb on my motor now.  If I buy another just like it, I can run dual Holleys.  Both options require adapter plates.  I believe both options will fit under my 55 TBird hood with small air cleaners. Will I have to mount the Holley carbs sideways?  I have seen some mounted straight like an FE motor.  Where do I buy linkage?   Do I connect both primary shafts together?

The Strombergs were favoured by many Tri carb fans years ago probably because they were original equipment on some models in the 1930s. There were 3 models made at one time & one was a  bigger unit but they are rare now. (the model #s escape me at the moment. But I believe the smaller one was a model #81)  As for variants on the Holley 94's, the biggest & only one with an auto choke was the 1956 unit used mostly on Ford 272s. I believe the venturie size is 1-1/16"...
N.B.- Don't  want to step on anyones fun, but if anyone here is looking to buy a  Tri-Power intake & expecting good perfomance from it, avoid the Y-Block Offenhauser intake. Tested by our moderator Ted's shop, it performed badly, finishing dead last of 7 tested..  


Paul