I know this is a dumb question but what is the cfm of the carb on my 83 z28?

 

If it's the factory quadrajet it should be 750cfm i think

 

All CCC carbs are 800cfm with the secondary air valve limited on some models not to open fully, thus reducing the max cfm it can flow. Grinding off the tang limiting the air valve travel, instant 800 cfm.

 

All factory Quadrajets on small blocks, CC or otherwise, are 795cfm. There are a few 850cfm units, but those only came on the big motors like some 454s and Caddy 500s.

That said, SOME had a little tab under the air doors that limit how much they will open, and cut cfm down to about 600cfm. Aside from the tabs, the carbs are still the same.

 

I think you're off by about 50 cfm. All qjets are rated at either 750 or 800 cfm. Maybe the actual flow is different, but 750/800 are what they are rated at.