On the weekend i installed a new (china) exhaust, now it was running fine that arvo but the next day it felt like it wasnt making full boost.

I dont have a boost guage yet but i took it too maximum motorsport and they plugeed there laptop in and took it for a drive and he told me its only making 10.5 pounds

my car is a my02 STI
the only other mod is a pod filter

has anyone got any ideas y this could be happening?

any help would be appreciated
cheers
pete