I love my turbo Del Sol.
My car never came from the factory turbo charged. I built my own turbo system.
As of right now my car gets over "10mpg city EPA" better then a stock
Del Sol, and closer to "15 mpg EPA" better freeway.
My BOV is open all the time until it sees boost. Then the valve closes.
So I never have any pre T/B positive pressure when the manifold is in vacuum.
At 5" hg or less you can here the BOV letting air out as Christ said. But on my engine it acts just like a N/A engine until you lay into it.
Now a adjustable BOV will only work with a speed density system. Mass Air systems won't like a open to atmosphere BOV.