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From mike@forgemotorsport on Vortex...
Completely irrelevant to someone's personal preference concerning sound or the engine management system's requirements for valve function.....
.... whether the air is vented to the atmosphere or recirculated is completely irrelevant to spool or any amount of “lag” supposedly created.
A valve exists in a turbocharged system as a failsafe against such a thing altogether.
"Lag" would only be created if there were no valve in place at all, and the residual charge air inside the intercooler piping "backed up" into the compressor wheel at throttle lift slowing it down.
Whether an atmospheric or a recirculating valve is used to discharge the residual pressure, either valve is still able to vent at throttle lift allowing the compressor wheel to maintain it's rate of speed, thus preventing any reversion of pressure and inducing any “lag” or having an affect on spool.
The discharged air being recirculated back into the intake side of the system will have absolutely ZERO affect on spool as opposed to an atmospheric setup.
The intake side of the system is under constant vacuum vs. actual atmospheric pressure (altitude), so the only arguement that could be made is that the vacuum effect acting on the discharged/vented air somehow keeps the turbo spinning faster than if it's vented to the atmosphere.
There is ZERO empirical evidence that one setup is more beneficial or detrimental than another in relation to compressor wheel speed.
If the use of an atmospheric valve is possible without any negative side effects concerning the engine management system of the application, as is the case on this vehicle, then it becomes purely a matter of personal preference.
