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?
You should call them and ask. I know the "670" street avengers have the same size venturi and throttle bores as a 600cfm 1850 too. Strange... Maybe it has to do with different booster designs or venturi shapes? Who knows.