12 Another important component on a turbo system is the blow off valve. Not to be confused with the wastegate, the blow off valve eliminates the pressure spike in the intake (cold) tract that occurs when lifting off the throttle under full boost. Closing the throttle abruptly while airflow and boost still want to continue into the engine results in a pressure spike in the intake tract. The blow off valve opens to allow this pressure spike to escape. Otherwise the pressure wave would reverse its path and attempt to escape back out the turbo (very bad for the turbo).