Ok, Im designing a closed loop catch can for my car. Gonna use a tradition style normally designed for open loop that uses the filter on top but gonna remove the filter and run a line going to the intake side on the compressor.
Now, Im sure that too much vacuum could be bad for a crank case with the amount of CFM a turbo would be pulling in. I was thinking of using a poppet style release valve similiar to Greddy's poppet bov. They are available to open in different levels of in/HG. Which one would I want to choose? I was thinking somewhere in the area of 5-7.

What are your guys opinions on this?

 

The more vacuum you can pull the better, but you still will have pressure in the crankcase. It takes a hell of a vacuum setup to keep vacuum in the crankcase under boost! Don't worry about the relief valve.

 

only way you'll get a large vacuum in the crankcase, is by using a vacuum pump driven by a pulley. can be had off summit for like 300-400 dollars.