There are spring kits and a re-circ kit available for those. The intent in adjusting a poppet or valve isn't to limit the amount of air that's exiting as that also induces surge (the whole reason for the BOV/BPV to begin with)... The purpose is to set the amount of vacuum required to open the valve. You should get the hardware to tune it OR run it re-circ and get over the "uber cool whistle", IMHO.
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