Carb/FI air meter flow (another new thread)

[Duke W.]

Hey it's just not fair that I light the bulb for all you guys on flow rates, pressure drops, and trips versus four-barrels and not even know the flow rate on my trusty ol' AFB equipped 327/340. I think I've heard 550 CFM, but with no pressure differential. Don't know how far back the industry standard 1.5" Hg. goes, but probably to at least the mid to late sixties. Does anyone have any data for the old AFBs and WCFBs of yore.

I think the Holley R-2818 in '65 was 600 CFM, and I've heard that there were two basic quadrajets - a 700 CFM model and 800 CFM. Does anyone have any flow rate at pressure drop data for these old carbs. A reference would be nice, but don't be timid, hearsay is acceptable.

In the 1957 SAE paper on the new FI system by Dolza and Duntov they quoted the air meter flow rate at 24 pounds per minute, but didn't mention the pressure differential. That's not uncommon for a paper on a new system. Sometimes they give data out of context, so as not to reveal all the features of the design. Twenty-four pounds per minute only works out to about 300 CFM at standard sea level air density which is about equal to what a 283/283 would aspirate at 4000 RPM. I don't think GM ever published any engineering data on the FI air meters beyond this, so it's a matter of whether or not they were ever privately tested and someone having or remembering the data. I think the late air meter design ('63-'65) may have flowed a little better than the earlier design, but, again, I don't have any hard data.

Duke

[motorman]

Re: Carb/FI air meter flow (another new thread)

duke holley lists your 2818 as a 600 cfm and the Q jets are 750 cfm with the 1 3/32" pri TB and 800 cfm with the 1 7/32" pri TB

http://clemz9@hotmail.com

[Ol'Geezer]

Re: Carb/FI air meter flow (another new thread)

For that matter, what is the rating on the R4555A on my '70 350/370? It looks like a 650 cfm unit, with the small, side-pivot float bowls. However, someone, a few months ago, claimed that it was an 800 cfm carb. I just can't imagine Chevrolet oversizing a carbuerator that much. The engine just can't use that much air.


Geezers Cars

[motorman]

Re: Carb/FI air meter flow (another new thread)

the holley book lists a R-4555 as a 780 cfm from a 1970 camaro 302 with std shift

http://clemz9@hotmail.com

[motorman]

Re: Carb/FI air meter flow (another new thread)

my error should be 350 not 302 i am used to z-28 being 302

http://clemz9@hotmail.com

[James F.]

Re: Carb/FI air meter flow (another new thread)

Duke, Don't know if this will be any help or not. In response to a letter I wrote regarding air flow of a AFB carburetor to Carter Carburetor Division, I received an answer dated July 1968. Carter answered a 3506S had a rating of 637 CFM at 2" mercury. I did not understand the 2" mercury bit, at the time I was trying to buy a Sears replacment AFB (listed for Chevies) for my Studebaker 3506S. Sears didn't mention anything about mercury! Regards,

[Duke W.]

Thanks, Jim! Big help.

In fact, it may be THE DOCUMENTED answer. From the prior threads you should now know that the two inches of mercury is the pressure drop across the carb required to produce the quoted flow quantity. We have also learned that we can convert to the "industry standard" 1.5 inches pressure drop for four-barrel carbs by multiplying the square root the quantity 1.5 divided by the actual pressure drop times the quoted flow,or:

CFM@1.5" = Sqrt(1.5/2,0) x 637 = 547CFM@1.5"Hg.

This rounds off very nicely to the 550 CFM number I've heard as the flow for the '62 to '65 327 AFBs, however, this assumes that the 3605S is basically the same carb. There was a version used on the single carb 409s that had slightly larger throttle bores/venturis which flowed a bit more. So can you tell me the TBs and venturi sizes of this carb. The 327 AFBs had TBs of 1 9/16" and 1 11/16" with main venturis of 1 1/4" and 1 9/16" respectively. If you don't have this data what year, engine, and Stude model was it for.

Now if I can only get Mr. Waggoner to add the capability to draw square root symbols, superscripts and subscripts, I can write a whole bunch more neat engineering formulas for all you car guys.

Duke