Duke, are the 1 bbl carbs rated at the same 3" standard as 2 bbl carbs? The information about 2 bbl carbs was very enlightening. I was recently looking at some 2 bbl Weber carbs for my Mustang 6 cylinder. The Clifford Performance catalog suggested carb ratings that appeared to be too big even for modified engines. Your info helps put the rating into perspective and the carbs are not as big as I thought.
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Re: Duke, CFM carb ratings
I thought about the one-barrel rating while I was posting my responses, but I don't know for sure how they rate them, however, are you referring to a single barrel carburetor like what is used on a basic inline six, or are you referring to a high performance Weber DCOE set up that provides and individual "choke" (as the English call them) for each cylinder?
Duke -
Re: Duke, CFM carb ratings
Yes, I was thinking about the 1 bbl carb on an inline 6 such as my Mustang or the 3 carbs on an old Vette.Comment
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Re: Duke, CFM carb ratings
the one barrel carbs are also rated at 3" hg. i convert to 4 barrel ratings by multiplying .71 X the 1 or 2 barrel rating. i do not know if this applies to webers.
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Correct
Multiplying the two-barrel rating (CFM at 3" depression) by 0.71 is effectively the same as dividing by the square root of two (1.414) to achieve the "equivalent four-barrel rating" (CFM at 1.5" depression). This is the best way to remember the conversion formula as it is a lot easier to multiply in your head by 0.71 than divide by 1.414 to get a ball park equivalent four-barrel rating.
I've never seen any flow data for Weber IDA and DCOE type carbs, but if we had numbers they would be huge for an individual runner system with one barrel per cylinder. This is because with an individual runner system the carb is only flowing about one-quarter of the time - only during the inlet stroke. Remember the four 58 mm DCOEs on the Grand Sports. That's about a 2.28 inch throttle bore for a total of 32.76 square inches of throttle bore area compared to 8.95 square inches for a 800 CFM Holley, so the four 58 DCOEs will probably flow well over 3600 CFM (steady flow) at 1.5 inches.
A properly sized weber should make more power than an single four barrel because the manifold can be designed very straight without curves, and there are no mixture distribution problems.
DukeComment
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Re: Correct
duke the numbers i have for webers are the following, 48mm 2v 37mm venturi 510 cfm ,40 mm venturi 560 cfm, 45 mm venturi 600 cfm. best i can do on these, never messed much with webers. also a stock carb for a 5 hp briggs flows 20 cfm,good to know if you are into kart racing!
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Re: My Weber Is the "Quadrajet" Variety
Or would that be a "Dualjet"? The Weber I am putting on the Mustang is an unglamorous 2 bbl progressive DGEV. It is the "Quadrajet" of Weber 2 bbls. The engine has that damned integral intake log on the head and carb mods are limited and I did not want to over-carb. I got tired of the factory 1 bbl. I've rebuilt it several times and the idle has always been poor. The idle is much smoother with the Weber and I have yet to tune it. I'm waiting on some linkage to adapt it to the existing accelerator rod. Thanks for the infoComment
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