"i'm thinking of running a Holley Double Pumper Classic (mechanical secondaries, and manual choke) and i was wondering what CFM to go with that would give a happy medium of power and fuel mileage "
"Holley" and "fuel mileage" in the same sentence???????
While I would certainly agree with the manual choke.
Most enthusiasts utilize mechanical secondary carburetors ONLY on dedicated race vehicles, NOT street vehicles.
What carb you use is much dependant on the configuration of the intake; but if the intake is set up for a spread-bore (best for street), I would suggest either a Rochester Q-Jet or Carter TQ. Either will give you as much power as the Holley, and a BUNCH more fuel economy. Both are "on demand" secondary carburetors.
As a general rule, the TQ would give about 3~4 percent more HP and fuel economy than the Rochester, but parts are more difficult to find. The decision probably comes down to which of the two you (or your tuner) would be more experienced in tuning.
Now, if this is a dedicated race only vehicle, I might have a different suggestion.
Jon.
