These specs are calibration specs.
When a 1964 or 1965 2GC Center Carb goes on the Rochester Products "Air Box", (the carb is installed inside an actual box, no air cleaner, and with Stoddard Solvent running thru the fuel passages), you get a flow number that has to meet a given specification at a minimum air flow in pounds of air mass per minute.
Same deal for the 2G End Carbs on all 3 years and the Center Carb on the 1966 engines. The specs are right on the sheets.
A Holley or Rochester Products Flow Stand is not the same thing as a Superflow Flow Bench that only passes air thru the carb. The Holley and Rochester Products Flow Stands SIMULATED the actual carb running on a engine at a given rpm (CFM) point.
Be it Idle Conditions, or under other conditions. Engine Dynometers were used to verify running engine carburetor performance using fuel flow rates thru the carb, air flow rates thru the test cell, and exhaust gas analyser information coming out of the exhaust.
So a CFM "Number" means little on a Engineering Build Sheet. They do list Pounds per Minute (Air Mass) specs though to make sure the Idle air/fuel is correct for the engine to idle properly.
Sean Murphy, former employer of Brad Urban, friend of Tom S, owner of Sean Murphy Induction, did a article on Rochester 2 BBL carbs about 10 years ago.
Here is the link. It talks about Carb CFM because racers like to talk to cfm numbers.
Carb Engineers, be them Holley Engineers or Rochester Engineers talk in lbs/min of idle air flow and Air Box "set points".
https://www.hotrod.com/articles/ctrp...g-carburetors/
I am diverging from posting the normal info, because the info I have been posting tells Carb Engineers, Rochester Products Engineers in this case, how to test on a Engineering Carb Test Stand a given carb to make sure it was acceptable for production.
Before people started racing carb CFM (vs actual Pounds per Minute of airflow at a agreed-upon test point), a Holley Air Box could test a Rochester 2 BBL and compare it to a Holley 2 BBL as far as pounds of air mass (using Stoddard Solvent as the fuel) one carb vs the other. Then the CFM racing started.
Autolite had their Carb Test Stands, Holley had theirs, (both at the Engineering Locations and at the Carb Build Plants.
Rochester basically did their Engineering/Testing in Rochester N.Y.
Read Sean's article, he is a good carb guy, better than most.
Tom V
No more History Lessons until I get all of the sheets posted.