This is an old question.
B block guys have discussed it, LA guys ignore it, and now I see \6 guys actually putting theory to use.
So, simple answers please, for some of our simple minds.
What is the advantage to two barrels over a well tuned single? (\anted applications)

This also opens up the 2 vs 4 debate. I have seen and been seen discussing the basics of multiple carbs (barrels) for many different vehicles. Every speed freak from boats to bikes to cars and even snow machines talk about it. But this site is the first I've seen actually put theory to use! Probably by necessity, but the info is still pertinent.
What say all?

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Mattelderca
78 NYB (gone now), two S series, three old Snow Cruisers and a Doo.

Actually the V-8 guys(and even non-EFI 4 cylinder guys) who are knowledgeable use it and dial it in as such.

The important part is about maintaining a good vacuum signal with proper flow... If the carb is properly sized then there will be excellent air flow through the venturi without a major drop in vacuum on opening the throttle plates, this keeps the fuel is suspension better and allows for almost instant response from the go pedal....also the higher vacuum allows more/better use of the vac.advance on the distributor allowing for more "economy"...

If you drive regularly with a vacuum gauge hooked up to the port that is fed from under the throttle plates where you can see the change best (and see what the carb is reading then reacting to), you can see how far the vacuum reading drops off when you open up the throttle plates...In the case of a single wide barrel all cylinders see it at one time, also to get more out of it flow wise the plate has to fairly wide open (you might notice on say a Holley 1945 when you punch the pedal at the green light the vac. reading can go down to 6"....by then you are in the power valve and using more gas to get it to go). If we used a BBD 2 barrel...the throttle plates do not have to be open so wide to match the flow that a 1 barrel has at say 1/2 throttle, this may also keep them closed enough that you may get the same response and see a better vacuum reading (maybe 11-13"+/-).... If we were to step up to a small 4 barrel, and we only used the primary pair, we might get about the same readings as the 2 barrel (we are only using 2 of the 4 barrels)...Depending on tuning of the secondary circuit (vaccuum opening, or mechanical linkage)...if the secondaries open too soon, the vacuum reading will flop (worse than the 1 barrel), if too late then reading might remain high but you won't get the use of more flow through the carb. Exception to this is the racer, who will be at high rpm and at launch the engine needs all the carb can give it....in which case the high rpm would keep the vacc. reading high if only on the primaries but needs to open the secondaries ASAP for power (along with the power valve enrichment, etc...)...

You can size a carb too big...in which case you would get poor mileage, "bogs" in performance and you'd notice that the vacuum reading would be very low because the venturi bores are bigger and take little throttle plate movement to equal the flow of the smaller carb....

Back in the good old days, carbs really weren't that big, so enthusiasts and some manufacturers faced with the fact that to get a bigger engine to breathe right needed to combine multiple carbs to get enough flow (literally a modern big block carter BBD would almost flow as much as one of the early Holley 4000's....you'd need 3 Stromberg 97's to get 500-600+ cfm for your flathead...Holley 4150 600 cfms weren't readily available yet...and once the biggest big blocks came around a pair of 600 cfm dual quads might be needed over the single dominator-and possibly meter better with the smaller bores).


After that you will start needing to read about different intake principles especially on why running 6 single carb on an IR setup is good for certain setups, but may get out performed by the single carb in others. Also your carb and intake choice may also be influenced greatly by the engine you are building, street vs. track (or...).


2 cents...

-D.Idiot

I can second that. Another reason for a single barrel may be ease of tuning. With 2, 4 3-2, 2-4 set-ups the more complex it is to tune and get running right. More carburetors may be a good thing for example there was a 50's prototype hemi with 8 1bbls and individual linkages. With more venturis and the closer the cylinder to venture number is the greater h throttle response.

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Leela: 1970 Dart 225 CID
Coulmn Shift TorqueFlite
7 1/4" Axle 2.76 Gears

Go ahead and save that weird car, the sedan, the 6 cylinder, the C-Body. If you want a big block musclecar and that's all you care about, your missing the point.