Compressor surge is when the air pressure after the compressor is actually higher than what the compressor itself can physically maintain.
This condition causes the airflow in the compressor wheel to back up, build pressure, and sometimes stall.
In cases of extreme surge, the thrust bearings of the turbo can be destroyed, and will sometimes even lead to mechanical failure of the compressor wheel itself.
You can run atmospheric or recirculated , just dont push the turbo out of its limits.
I have been running atmospheric Blitzz BOV for over 5 yrs no problem, my car does not smoke , nor does it stall, RPMS do go down from a fast cruise to a stop but it stabilizes on its own .
I am also running a JWT 4 bar ecu, and JWT says only run recirculated,
A Blow Off Valve (BOV) is a valve that is mounted on the intake pipe after the turbo but before the throttle body. A BOV's purpose is to prevent compressor surge. When the throttle valve is closed, the vacuum generated in the intake manifold acts on the actuator to open the valve, venting boost pressure in order to keep the compressor out of surge.
Bypass valves are also referred to as compressor bypass valves, anti-surge valves, or recirculating valves. The bypass valve serves the same function as a BOV, but recirculates the vented air back to the compressor inlet, rather than to the atmosphere as with a BOV.