booost set at 20psi falls to 15psi by 7000 why?

[96whitetalon]

I have a big16g with 3in turbo baack exhaust, 550, safc ect any ways...I have my boost set at 20psi and it hold there until about 5000rpm and it starts to fall off and by the time it hits 7000rpm its at 15psi..There is no shaft play in the turbo, it does have little damage to it casued by when i blew my motor some pieces of pistion ring went thought it but the wheel still look pretty good (8 out of 10)..so do you think that can be the ploblem or could there be more to it

 

[exzercist]

if the wheel isnt in top shape youll prolly losin effiency on ur turbo.

 

[RiceKiller_TSi]

Sounds like the ever popular boost leak to me. Make a boost leak detector. And find that leak. Could also be a weak BOV.