Depends on the carb. The rochester Q-jets had a spring loaded air flap over the secondaries. The carb would only give the engine what it wanted according to vacuum demand. The airflap would open progressively at full throttle on a small motor, to keep the airspeed thru the carb venturis at a high enough speed for a good mixture independant of RPM. The Q-jets were all rated at 750-800 CFM, and were factory equipment on everything from 305s to 455s. They were just factory calibrated for each application.
On the other end of the specturm is the Holley manual secondary models. When you mash the gas, it opens all 4 bbls at once with no airflap. Manifold vacuum goes to squat, resulting in a huge BOG until the motor RPMs catch up to the carb's throttle position.
Some edelbrock carbs operate on the same principle, so see if your carb is a Q-jet replacement or a Holley replacement.
I must respectfully disagree with Mr. Lincoln on one point.
The Performer (not RPM) manifolds are equal or superior to many chevy stock intakes in weight and port CFM. They can provide a slight HP increase on a stockish motor with a significant weight savings. The RPM model will hurt your low-end torque below 1500 RPM. But you'll see gains in midrange and top end with proper cam and valvetrain selection.
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