It's not 0-7psi instantly.
Prime example is high way speeds, if you are cruising 70mph a little over 3 grand the car is pulling 15" of vacuum, the moment you push down on the accelerator it goes to 0psi and climbs from there as rpms build.
Now taking off from a stop the car will go from 20" of vacuum at idle to 1-2psi initially and will stay there until the mph has leveled off then it goes back into vacuum and you can hear the bypass "whoosh" pretty much all the time while its in vacuum at low speeds.
-Mark
