[Steeveedee]

Originally Posted by HO455

Well technically that isn't true. Due to internal GM rules and issues there were Quadrajets that left the factory as 650 cfm units. Most notably the 400 ci first gen Firebirds. The exact engine in a GTO made 350 HP but in the Firebird it made 335 HP. The carburetor was the same on both engines with the exception that the secondary throttle shaft was limited to prevent full throttle. So yes both throttle bodies were capable of 750 cfm but unless you modified the secondarys you wouldn't be getting 750 CFM. There are more strange exceptions but none of the are very common. Like a Q-jets on 230 ci engines. To run them on these small cubic inch engines there are physical internal differences from the large cubic inch engine carbs that relate to idle quality and low rpm throttle response. It is easier to find a carb that started life on a similar sized engine unless you are aware of the challenges you are facing. In your case the 800 cfm units came on 454's from the factory. In fact I believe it is the most common application of the 800.

Many 455 Firebirds had the 800 CFM carb as well.