is there anything to suggest said boost? i.e boost gauge?
if its not chipped the boost will cut off after 9 or 10 psi iirc.
also i would strongly suggest not touching a boost valve yourself as turning the boost up or down also requires fueling, timing etc to be compensated for the higher airflow on mfi models as the metering units are quite old.

also what turbo is fitted?, as im just thinking why fit a bigger turbo but not get it chipped, as the bigger turbo will not be able to run anymore than standard boost so all you'll gain is more turbo lag??! :s