Is a blow off valve required for a turbo system?
No. For low boost applications (e.g. 7psi and under) its not necissary to have a blow off valve, though it is recommended. Under boost, when you let off the gas and the throttle plate closes, all of this flowing air suddenly comes to a halt, and is forced backwards, back out the turbocharger which normally creates a fluttering sound. This sound is called compressor surge, and although at low boost pressures it doesn’t cause as much damage, it still is bad for a turbo’s health and lifespan. Most mitsubishi type turbos are built to be able to handle this low boost without a blow off valve just fine. You will however get more performance with a blow off valve. In between shifts the blow off valve keeps the turbo spinning so it can continue where it left off, as opposed to the turbo being slown down from the surging.
