If you increase the valve pressure (turn in the screw), you increase the valve's resistance to opening at lower vacuum levels, meaning part throttle or at idle but you also increase the occurrence of compressor surge, which is what a BOV is there to prevent in the first place.
Hi guys;
Those of you that like to tinker with diy... have a look at this.
http://www.charm.net/~mchaney/homedyno/dynokit.htm
You may have a better idea to make it run cheaper on you own effort.
You can also do...