often i fine the car feels more laggy with the dump valve

the idea of a dump valve is to protect the turbo, in some cases the force of the air going back through the turbo when the throttle is closed can cause damage to the comp wheel or stalling the turbo causing the nose nut to come off.
i don't normally run a dude valve, 34psi on my escort was no problems with out one, but some turbo's can take it, some can't.