The original Economiser or Power valve used in the Holley 94 Carb opened at 7.5in Hg vacuum. These Power valves are identical to the current valves used in modern Holley Carbs (eg Holley 650, 750 Quad carbs, etc) and are available nowadays in a variety of vacuum ratings, or even as a blank-off valve that doesn't open. They come in 2.5in Hg to 10.5in, and going to a 5.5 or 6.5 is handy to eliminate valve recession and burnt valves with modern unleaded fuels, but fuel economy will suffer, and if you should be running twin carbs on your Ford then going to 4.5 will be necessary to get them to open at all!
BTW, if you should also need Main Jets for your Holley 94, these are also identical to the Modern Holleys (and therefore readily available), and are a .051 size as standard.
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