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around 20" at idle, tapering off to nuthin' at WOT. Alot depends on what you happen to be doing at the time. Engine load plays a big factor in manifold vacuum.
How old is your filter, if your still seeing vacuum at WOT she isn't breathing as deep as she could. Come to think of it with a stock air of my truck never got to zero, but my mustang with a cold air did at the time