What is a blow off valve, dump valve and waste gate?
A. When you take your foot off the throttle to slow down or change gear a flap called the “butterfly” closes and stops the flow of air into the engine. The turbo though will still be spinning and thus tries to pump air in, but can not and rapidly slows down with the restricted air flow. When you reapply the throttle the butterfly is opened and the restriction is removed and the turbo can again increase in rpm to develop boost. This time difference is felt as turbo lag and in the situation above would be quite crude. What a blow off valve does is detect a vacuum on the engine side of the butterfly (throttle off) and opens a valve to dump excess pressure back to the inlet filter. This reduces the restriction on the turbo allowing it to almost free spin and not slow down as quick. Then when you put your foot down, the butterfly opens and the blow off valve closes. The turbo still spinning quite fast takes much less time to spin up to full boost and thus creates less lag. If the blow off v
