I've fitted a piston type dump valve to my EFi managed escort turbo and the only problem seems to be that it hisses all the time until it comes onto boost I can't say I've ever noticed this before when I've been in other turbo'ed cars.
Anybody got any idea whats up?
you need a stronger spring in there mate, give forge motorsport a ring, they have about 5 different strength springs depending on your boost level.