When you open the system up and let it breath better it tends to drop the boost but that isn't necessarily bad. Sometimes high boost is actually cavitation. The sc is just spinning and making pressure but it backs up instead of flowing thru the engine. Lower boost pressure that is useful is better than higher boost that isn't going anywhere except maybe out your blown head gaskets. My engine is opened up and can use 14 psi of boost but a stock or mildly moded engine might be better off with only 8. It seems like the GTP's only run 8 psi, also.