The Jalopy Journal
Discussion in 'Traditional Hot Rods' started by Omarsvette, Nov 25, 2020.
Good point, then ventri??
Thank you makes sense...so really .97 and 1.03 is nothing in comparison of the two ventris. Maybe 10cfms? I don’t think .06 “ is gonna make a difference in my set up. If the bores measure the same...
^^^correct me if my thought process is wrong...
The difference between a 48 and a 97 is 22cfms. Times that by six and you've increased the total cfm by 132. I think mixing and matching the carbs might make it difficult to balance them all evenly.
Your 354 motor needs around 500 cfm using the standard volumetric efficiency formula. With 6x97s, you're around 930 and with 6x48s, 1,062.
I feel you. 500 cfm could work for my hemi but the original wcfb is less than that for sure. My 331 hemi has two wcfb and it doesn’t run rich, if anything a little lean by spark plug color. My current set has only one 48 (if it is a 48) so I don’t know how much difference that would make especially if I us it at the rear, which I could make come in later with progressive linkage. I also wonder if it’ll make harder to balance. I could run it like that and pull spark plugs for a report. I’m sure I’ll get another 97 to replace it. I’m not sure if the sum of the cfm is equivalent to total cfm, I’m not sure if they add up to a higher cfm. Like two 650s equal 1300 total cfm. Or does it?
A few thoughts:
(1) CFM is definitely NOT an additive property. The total CFM available from any multiple carb set-up will be a function of BOTH the carburetor size AND the intake manifold design. For the most efficient systems, the number of carburetor barrels should be an even divisor of the number of cylinders. Thus 2x4, or 2x2, or 4x2, or even 8x1 have a better chance than 3x2 or 6x2 on a V-8. Of course, with eye candy, more is better
(2) PotvinV8's comment about mixing and matching carbs of different venturii area; then trying to balance them is spot on. The biggest reason (today) in the use of multiple carburetors (other than eye candy is better cylinder fill density balance. Different size carbs do not help this. 80 years ago, the biggest reason was cost.
(3) Stromberg produced several carbs marked "97" for Ford. The bare center castings were basically the same internally BEFORE machining. Everyone knows about fuel jets, but air jets, bypasses, restrictors, etc. should all be taken into account for absolute best results.
EDIT: This thread started as a thread for carburetors for a basically stock street engine. For street use, balance and venturii air velocity are much more important than maximum CFM. MUCH easier to make carburetors race well (WOT consideration only) than running on the street (idle, off-idle, various vacuum values, RPM transition, etc., in addition to WOT).
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