I understand that there is a difference between how four- and two-barrel carburetors are rated, related to the vacuum used on the flow benches. Are one-barrels rated at the same vacuum as two-barrels? And are the advertised ratings to be believed, or used as a basic comparison for similar carburetors?

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

Yes the 1bbls are rated the same as 2bbl.......... 3.0inHg vs 1.5inHg for 4bbls

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Ah ha, I see. I was (retardedly) thinking that the front and back sets of cylinders fired together, rather than the 180* apart that they truly are. (or something along that thought process.) Duh. Realistically, how much air is one cylinder going to pull?

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Used to own:
'82 Dodge D150
Erson 270 Cam, O/S valves, mild port work, ~9.5:1 compression

Currently fighting with an '85 VW Cabriolet

My other passion

225 cid/6 = 37.5 cid

At 5000 rpm that translates to approximately 54 CFM at 100% VE, so it is actually probably closer to 40 CFM (@ 5000 rpm...)

Hmm.. yeah.. I don't think enough before I ask questions. I was trying to figure the math behind it and /almost/ asked another question before I realized that it revolves twice for each intake stroke. Once again, duh.

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Used to own:
'82 Dodge D150
Erson 270 Cam, O/S valves, mild port work, ~9.5:1 compression

Currently fighting with an '85 VW Cabriolet

My other passion

But the flow isn't even (think sine wave)...... So the instantanous flow (or peak flow) will be higher so that on average it's 40cfm....

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Follow this...........

1 cylinder needs 54 cfm at 5000 rpm.

Assume the intake stroke lasts 240 degrees.

So to average 54cfm during the 4-stroke cycle, the carb needs to flow (720/240) * 54cfm = 3 * 54cfm = 162cfm to average 54cfm.....

During that 240 degrees of intake flow, the flow isn't constant....

As an approximation, figure the flow rate is like a sine wave (think AC current, where the average is 120volts, but the peak is higher (1.4 times higher))

so

at peak flow you need a carb that can flow 162 * 1.4 = 227cfm.........

BTW, with the same 240 degrees intake duration, the 227cfm carb would work with 2 and 3 cylinders as there's no overlap during intake cycles.

BTW2, and the 227cfm carb would even work with 4,5,6 cylinders with 240 degrees duration because when 1 cylinder needs the 227cfm, other cylinders need 0cfm.

BTW3, a 6 cylinder would have constant flow of 227cfm

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

so what your saying is a dual 1bbl setup that flowed 227 cfm out of each carb would meet the peak requirements for the motor.

or are you saying a 2bbl setup that flowed 227 cfm would have sufficient flow.

what are the carter bbs carbs rated at?

I'm starting to understand thanks emsvitil

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64' Valiant Signet 5.9, 64' Dart 170 moredoor 3.7, 67' A100 3.7, 00' Dakota SLT 4.7

I think he's saying dual singles that could deliver "113.5" each would get the job done.

Nope......

At peak flow 1 cylinder needs 227cfm (with the above 5000rpm example).. On average 1 cylinder needs 54cfm, but flow isn't constant, so a carb rated at 54 would choke the engine.

I think a BBS is about 200-220cfm.


Any carb with 227cfm will meet the flow requirements on a single or split manifold (with 6 or less cylinders). The advantage of the 2bbl carb is that they flow more air, and there's less restriction to the flow getting into the engine. Less restriction, better volumetric efficiency, more power.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Last question I promise. Is their any real advantage to go with 2 1bbl's over a single 1bbl? Besides the fact that they look cool and would be easier to install on my 64' then a 2bbl.

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64' Valiant Signet 5.9, 64' Dart 170 moredoor 3.7, 67' A100 3.7, 00' Dakota SLT 4.7

Don't forget that the twin-carb manifolds have balance pipes such that they are not truly "split".

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Look cool? Here's an idea Get 3 carbs and put 2 of them on believable mockup manifolds - one on each side of the real one.

If I could find some really cheap (read plastic) carb stacks I'd put 6 of them on a mockup just to see the first look on a couple faces when I pop the hood.

Been done

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一期一会
Too many people who were born on third base actually believe they've hit a triple.