What causes Boost creep??

[GreddyGst]

I almost positive i have boost creep, my gauge reads 25+psi when I WOT. I have read the threads about boost creeping and thanks to OLDMAN I plan to port the turbine (turbo inlet & area of the flapper). I heard that what causes the boost creep is the 3" exhaust system we put in our cars... I too have 3"catback exhaust / 3" test pipe / 3" Downpipe... What I don't understand is why don't turbo manufactures port it to the point where there won't be any boost creeping even if you put a 3" exhaust system? or is there a problem if they port it and you use stock exhaust? I'm not gonna drive my car for a while till I take out the turbo and port, but could someone explain why the exhaust makes my car boost creep and solving it with a port job?
Thanks for any help.

 

[99gst_racer]

but could someone explain why the exhaust makes my car boost creep and solving it with a port job?

Creep is caused by the exhaust flow path outflowing the wastegate flow path. And that happens when the size of the exhaust flow path is too efficient or when the wastegate flow path is too inefficient.

A 3" turbo-back exhaust raises it's efficiency so that can sometimes cause creep. And a small and unported turbine housing/wastegate flow path can also lead to creep; thats why porting it can help.

 

[GreddyGst]

Thanks for that explanation .