CFM ratings on autolite carbs??

[wsa111]

Are the CFM ratings for the 2bbls @ 3" or 1.5"??
How about the 4bbl flow ratings are they the same or at 1.5".
Why i ask all i see is high flow ratings for such a small venturi.
The annular discharge nozzle takes up a lot of the flow, but seems to make up for the loss via better fuel atomization.
CZLN6 would definately know.
http://home.alltel.net/bsprowl/Autolite4100Test.htm
This is one link i found. Bill

 

[MustangSix]

SAE test standards are different for each. 1 bbl and 2 bbl carburetors are tested with a 3 inch vacuum. 4 bbl's are tested with a 1.5 inch vacuum.

I.e., the CFM tests for 1 and 2 bbl carbss are done with the flow bench sucking twice as hard.

To compare CFM ratings between 1/2 bbls and 4bbls, multiply the 1/2bbl rating by 0.707.

At the same pressure drop, a 500cfm Holley 2bbl flows 353 cfm, or just slightly less than a 390 4bbl.

 

[shmoozo]

SAE test standards are different for each. 1 bbl and 2 bbl carburetors are tested with a 3 inch vacuum. 4 bbl's are tested with a 1.5 inch vacuum.

I.e., the CFM tests for 1 and 2 bbl carbss are done with the flow bench sucking twice as hard.

To compare CFM ratings between 1/2 bbls and 4bbls, multiply the 1/2bbl rating by 0.707.

At the same pressure drop, a 500cfm Holley 2bbl flows 353 cfm, or just slightly less than a 390 4bbl.

Ah, so by my math, a Holley 350 cfm 2bbl would flow about 247 cfm at the lower vacuum where the 4bbls are tested and a pair of them would flow about the same as a 500 cfm 4bbl, albeit with a somewhat more complex throttle linkage and intake manifold arrangement.

Got it.