Exhaust Vacume question

With a breather on the valve cover I only got 1.5 vacume at idle and 2.5 at 3000 rpm.Sealed the cover and got 3 at idle and 5 at 3000 rpm.Vacume gauge sealed to dip stick tube.Will leave it hooked up and see what it reads going down the track at 6000 rpm.Thinking about a vacume pump cause I would like 10 neg pressure constant.