If you have my book the maximum open point is discussed in the Chapter on Edelbrock carburetors.
When we did cfm testing the entire stop was ground off and an adjustment screw installed so we could continue to adjust the flaps past 90 degrees to find the optimum open point, and when going any further made no improvement or diminishing returns.
I backed up the cfm testing with dyno testing using the adjustable "stop" and it confirmed what the air flow testing did exactly. Going too far open not only doesn't improve airflow, it starts to impede/redirect fuel flow from the secondary nozzles as well. This testing was done over 40 years after the 1973 information was printed.
It would be unlikely that any of that sort of testing was done way back in 1973 and why the cfm ratings are less than what we came up with.......IMHO......
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73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
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