I agree with the above. Just to try to clarify my point: if a carb is rated for XXXcfm and you motor needs YYYcfm, by definition if XXX=YYY there will be a 1.5" pressure drop across trhe carb. There is only a couple percent hp to be theoretically gained by decreasing this pressure drop to say, 0.5". And it will some very careful tuning to get the carb to work right with only a 0.5" drop. A vacuum seconday carb is best for street cars because the secondaries only open as much as "needed", this helps avoid the terrible "bogging" that often results when using a large mechanical secondary carb.

Bottom line: a vacuum secondary 750 is great size for a street 350.

Rich