Originally Posted by sedanbob
My turn-key ZZ4 crate motor came with a Holley 750cfm dual-feed, with vac secondaries. Some guys on another forum think that is too big for a ZZ4 on the street, and recommend a 600cfm instead, claiming it will be more responsive and still deliver power. I believe they are thinking about a double pumper. When I suggest that I am mostly running on the primaries, and the vac secondaries will open as required at higher rpms, I don't get any answers.
Does anybody here know what the cfm flow of just the primaries might be? I have searched all sorts of Holley specs, but can't find this particular spec. The engine seems very responsive to me, with no lags when I put my foot in it. The newer ZZ4s now come with a 770cfm Holley.
It depend on the final gear ratio you have and how big the cam is. If you have 4:10 a 750 will work. If you got 2:43 gears. You may have some bog or slow response. Then you need a 600 CFM carb to make it work. The bigger the cam, the less torque at the low RPM range resulting sluggish throttle response. Every component must work together as a whole, not just the carb.
Chevy used 780 CFM on 302 and 350 Z/28 Camaro's. I would not worry about it.