Well I just found the answer in my Holley technical books. Charts too. I'll post them if anyone is interested. The presence of an air cleaner restriction increases venturi vacuum and causes the secondaries to open sooner
in all cases. What caused me to ask the question was the fact that I monitor how much my secondaries open via a zip tie on the shaft. After putting in my low restriction X-treme top, my car runs better,
but my secondaries open less. I was quite surprised at this. What it also means is that I need to change the spring that controls the secondaries now so I get the full benefit. I can't remember what I have in there either. I think I'm going to try the Quick Fuel adjustable secondary vacuum housing. It just bolts on and then adjusts when the secondaries open with the turn of a screw.
