A note on CFM, from a question I answered recently on another site:
The actual CFM from the Quadrajet carburetors are application specific. They basic castings come in two flavors, 750 and 800 cfm. As delivered they can vary considerably from those numbers depending on how long the stop is on the secondary airflap shaft to limit the opening angle of the airflaps in the airhorn.
The factory also limited to open angle of the huge secondary throttle plates in the baseplates on many applications to limit cfm as well.
Good examples of this are early Firebird carburetors that were delivered on the 400 engines. I've seen this quoted many times as done for "insurance reasons", but for whatever reason for sure they limited the open angle of the secondary throttle plates and had a longer stop to limit the air flap open angle as well. This is mentioned in several sources in print on early Pontiac stuff.
Anyhow, the factory also made some higher CFM models in 1971 as mentioned. They basically took the standard "750" cfm castings and removed the outer booster rings to increase cfm. Those castings are also "dubbed" 800cfm, but actually testing puts them at 827cfm.
At the same time Rochester released the first larger castings for the 1971 Buick 455 engines. They are also dubbed "800" cfm but use a short stop on the secondary airflap shaft and flow 849cfm.
The larger castings showed up for Pontiac in 1973 and were released on the 455 Super Duty engines, part numbers 7043270, 7043273, 7044270, and 7044273. Those were also produced as Service Replacement part number 17054910 and 17054911.
Edelbrock came out with a line of Q-jets and their 1904/1905 were dubbed "800" cfm and the 1910 were advertised at 850cfm. The 1910 is the EXACT same casting as the 1904/1905's just has a shorter stop to allow the secondary airflaps to open to 1.270" (just a little less than .100" when compared to the 1910's) as shown in my book.in my book on page 118.
There is also information on how to make a large cfm q-jet by removing the outer booster rings on page 116. I've done quite a few of this at this point and have supported over 700hp successfully with them in full race applications, these will flow apprx 897cfm.
I'll add here that Edelbrock patterned their 1904/1904 and 1910's after Chevy truck Q-jets produced in 1979-1980, and they are nearly identical to part numbers 17080212 and 17080213.
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