Quote:
Originally Posted by streetstar
Why only 650cfm? A stock Q-jet is 750cfm. The carburation needs to be tailored to the demands of each particular engine.
---a 350 is well suited to a 750. A smaller engine like a 305 or 307 can make use of a 600 or 650 --- but a 383 stroker, or a built 400 might be fuel starved with a 750 even. A friend's 383 makes close to 600 hp's on the dyno with a Holley 930dp, and could use more so he is going to a 1050 dominator .
A 750 quadrajet has small primaries for good torque and efficiency on the street, but has large secondaries for full throttle performance-- that is why it is made on a spread bore, whereas the Holley primaries and secondaries are externally the same size .
GM engineers are relatively smart-- they wouldnt spec the 750 qjet if it was a total dog
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Yes the typical Q-Jet CAN flow up to 750 CFM. The way the secondaries are designed though, that doesn't always happen. The secondaries and secondary metering rods on the Q-Jet are designed to flow only as much air and fuel as the motor needs. A 305 or 350 will not pull 750 CFM through the carburetor. They went with this design so a single carb body could cover a large range of displacements and power levels.