Because the original conversation is taking place in the classifieds, I have taken the liberty of making a new post.
 
When it comes to picking a carburetor for an application, carburetor sizing is only one piece of the equation.  Fuel atomization is a bigger consideration and much of that has to do with the emulsion channels and discharge nozzle design within a particular carb.  Holley makes a multitude of 600 cfm carburetors with all of them varying to suit various applications.  The same is true for the 1.08 and 1.12 Ford carburetors as those were tailored for specific applications.  One of the big advantages to the older Ford/Autolite carbs were the annular discharge nozzles which provides much better fuel atomization at the venturies than the more common straight leg and drop leg discharge nozzles.
 
One of the big pluses to running a vacuum secondary carburetor is that the secondaries are demand driven meaning they only open the amount required for optimum performance.  This means that by intentionally oversizing a vacuum secondary carburetor for an application, it will never be undersized as the secondaries will only open the amount required by the engine.
 
To prove a point, I put a 1050 cfm Holley with annular discharge nozzles on my E4 cammed and otherwise stock 272 and drove it around for awhile.  Ran just fine but was obviously on the big side if the throttle was opened up fully at low rpm.  That car currently has the 500 cfm Summit carburetor on it which is slightly undersized but is a good driver otherwise.  For most warmed over Y’s, a vacuum secondary carburetor being sized at 750 cfm proves to be adequate for those rpm sprints up to 6000 rpms.  Keep in mind that most four barrel carburetors if just being daily driven will be operating on the two primary barrels that equate to a cfm rating that’s smaller than just running a two barrel carburetor (the older three bolt two barrel carbs are excluded from this statement).

Lorena, Texas (South of Waco)

Ted, I have a Holley 1848-1 465 cfm carburetor on my Tbird.  The off idle response is quick and drive ability is great,   Do you beleve I would I gain any noticeable performance with a larger carburetor?  Just curious.  Thanks for your response. 

I was curious because I have heard that annular discharge nozzles were a better design

SE Wis

Florida Phil;  Would you benefit from a bigger carb, probably depends on whether or not your engine is stock or warmed over. I'll leave Ted to comment on that if he wants ... Anyway, in Ted's test of "16" carbs on his warmed over 322" Y mule,  your 465 Holley  was in 4th place, just a hair ahead of a 1.08 venturie Autolite. The two 1.12s were back some from that..  (note; a few of the carbs tested were race prepped units)  


Paul

My TBIrd engine is a fresh .060" over 292 with "G" heads, iron 4V intake, Centrifugal advance ignition and an Isky 301333 cam.  My Tbird has it's stock three speed with O/D and a 4.11 gear.  It's a fun car to drive and very lively.  I drive the car often and don't wish to break down on the side of the road.  I have tried multiple carburetors and they come with issues that I would rather do without.  If going to a bigger 4V carburetor would provide a boost I could feel, I would do it.

I am running stock 1957 iron exhaust manifolds and a stock TBird exhaust system exiting out the rear bumper.   I believe I would gain HP by going to headers. The exhaust in these TBird runs through the frame.  It's a tight fit even with the stock system.  I have thought about using bigger tubes and dumping the exhaust out the side.  I don't know if headers would help that much.

Like all hot rodders, I am always tinkering with my car.  I believe I've exhausted all the stock upgrades.  I'm looking for the best bang for the buck as long as it doesn't sacrifice reliability.

What the dyno sheet does not tell you about carburetors is how it drives on the street.  While the driving part can be simulated on the dyno, the sheet itself just gives the full throttle or wide open information for the carburetor.  Smaller carbs that do well on the dyno may have fuel curves that are not happy for street driving but the same can hold true essentially for all carbs regardless if small or big.  All aftermarket carbs are universal in nature and may require some tweaking to get them where they drive around without hesitation, surging, lean and/or rich issues.  When testing the engines on the dyno, its an easy process to run them at part throttle and with partial loads to insure that they will drive fine once in the car.  Tailoring the fuel curves, accelerator pump shot, power valves, and jetting are just some of the areas that carburetors must have adjusted to get those driving characteristics happy.

Holley did a great job with the metering in the List 1848-1 465 cfm carb in that it’s a good all around driver with snappy low end performance but by the same token it's not a universal carburetor.  That carburetor was designed as the bolt on replacement for the 1957 Thunderbirds so it’s no surprise with it being happy on the Ford Y engines in general.  With any Y that has been warmed over, there’s some peak horsepower numbers to be gained if going with a larger carb but the engine would need to see in excess of 4800-5000 rpm to both feel and see that performance increase.

As a general rule, Ford was notorious for under sizing the carbs on their run of the mill engines.  I suspect much of that was to keep the rpms more or less in check which would reduce the number of warranty claims.  All the 4V offerings in 1957 had carbs in the 400-410 cfm range but it’s interesting that the dual quad setup in 1957 using the same heads and camshaft as the 245 HP 312 was rated at 270 HP.  That’s a 25 HP step up in power from just a cfm increase.  That shows some of the potential for those Ford Y engines.  As I’ve come to find with dyno testing those older oem stock engines, it takes a fully blueprinted and running at its best stock engine to match those factory horsepower numbers.  This tends to hold true for all makes and models of that era.

Lorena, Texas (South of Waco)

Note:  I was writing what follows while Ted was posting his.    Ted's reply has more meat to it than mine!

Paul.  Ted's carburetor performance test results were interesting, but did not provide insight about carburetor low speed performance, throttle response, drive-ability, or fuel economy and the like.  My recollection is that Jon Enyeart, the deceased original owner of Pony Carburetor, was a big proponent of the annual ring discharge design utilized with the venturi boosters in the Autolite 2100 and 4100 carburetors.  Like the Summit 4 barrel carburetors, the '56 Ford ECG 6 two barrel carbs used this style of venturi booster, also.


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

Florida_Phil: I think your 465 carb contributes a lot to the fun factor driving your setup. A small venturi carb develops a very strong vacuum/venturi signal very rapidly which equates to instant throttle response. Something electronic fuel injection could not duplicate. I'd love to hear from Ted how a larger carb, in your setup, may benefit the top end curve as I'm considering going back to my smaller Quick Fuel. It did seem to have more rapid throttle response than the 600 Holley I'm presently using. Just my 2 cents, JEFF......................


64F100 57FAIRLANE500

Selecting the right carburetor relies totally on the intended purpose and expectations of the vehicle on which it is being used.  For stock vehicles that are driven normally the majority of the time, carburetor sizing is of little consequence other than the carburetor being a good all around driver.  The engine has to start well when cold and be smooth in operation once it’s warmed up.  As the engines are being pushed into the higher rpm bands for various reasons, so too then is the need for larger carburetors.  While stock engines can benefit from slightly larger than stock carburetors, any modifications to engines that improve the air flow will require significantly larger than stock carburetion in which to capitalize on those air flow modifications.
 
I have included below the dyno results of a 272 tested with the 1957 312 ECZ Ford carburetor versus that of the Summit 500 cfm carburetor.  The cast iron intake manifold being used was also from a 1957 312 Ford engine.  While the full throttle performance of the ECZ carb was okay with the factory jetting, that particular carb had a noticeable hesitation on the ‘throttle up’ which was alleviated some by installing richer jets in the primary side.  Unfortunately the power numbers went down with the jetting increase so at the cost of fuel mileage and peak power numbers, some of the hesitation issues were reduced but not eliminated.  Disassembling the carburetor could find no obvious issues in where the problem was so in lieu of going into the air bleeds, a call to the customer was made.  In talking with the engines’ owner, this ECZ carburetor had the same hesitation issue in the car prior to pulling the engine for a rebuild.  Hence the purchase of a Summit brand carburetor.  The Summit carburetor on the other hand ran good out of the box with no changes and the fuel mileage is expected to be good.
 
A complete article on this 272 build will be in a forthcoming issue of The Y-Block Magazine which will go into the details on how the power numbers were able to exceed those of the 1957 312 engines without having to port the heads and sacrifice any low end performance.  This engine will still run on 87 octane fuel and be happy.  I still recommend using premium grade fuel in all carbureted engines only due to premium fuel having less ethanol content than the lower grades of fuel.  For those cars that sit a majority of the time, the premium grade of fuel also has a slightly longer shelf life.
 

 

Lorena, Texas (South of Waco)

This has been interesting reading especially the 2 dynos runs. With the Ford carb the peak torque was 270 at 3000 and the Summit had the same 270 at 2500 right where most of us drive our cars whether an automatic or stick. I realize we are not wide open at every light. :<)
I'm sure my old dual quad setup is terrible at 2500 running on the back carbs front barrels even tho it has always been snappy off the line when the signal changes just staying on the back carb.
I am always considering going back to a single 4 barrel and it would be a Summit from all I've read here and the Y-Block magazine but my set up has been pretty consistant and fool proof a long with its looks so I just hold off.
Once again thanks guys...

56 Vic, B'Ville 200 MPH Club Member, So Cal.