Do you happen to know what the venturi and throttle bore diameters are on a 670 and 870 street avenger carburetor? From what I've seen, they are much smaller than their 'cfm rating' would suggest.
What gives here with Holley? According to the size chart the only difference between the 870 and the 750 is a sixteenth in the back venturi the 750's way ?? Unless I misunderstood the chart?