If you are measuring your pressure with a T/C gauge, if you even half competently hooked up your system the gauge should zero out well before the pump comes up to speed. You will need an ion gauge.
Start up of a turbo system is easy. Turn both the turbo and mechanical pump on at the same time. The turbo will come up to speed as the system pumps down.
Most recently manufactured turbos can take some amount of air inrush abuse but there's always the killer Nth time. When you are ready to vent, turn off the turbo and let it wind down before venting.
Steve
Created on Friday, March 16, 2001 7:18 PM EDT by Steve Hansen