>I'm asking for a friend.. I don't actually know what a pop-off valve
>is, but apparently it's desirable in some way.
It is also known as a blowoff valve
>1. Is it legal in STX?
No, unless it is OEM.
>2. For my own information, what does it REALLY do? I've heard some
>"fast and furious" explanations, if you know what I mean, but I'd like
>someone with some understanding of the English language to show off how
>much they know on the subject to help my friend make an informed
>decision.
OK, I'm gonna assume you know the basics of turbo operation (exhaust-driven
turbine that compresses intake air)
In a turbo system without a blowoff valve of any kind : when you slam shut
the throttle blades quickly, there is a buildup of pressurized air in the
intake path (i.e. between the turbo and throttle body). This pressue has
to be released somewhere. Without a blowoff or relief valve, it'll "revert"
air back into the turbo turbine fins. This doesn't do the blades much
good, plus it tends to slow down the turbo rotational speed (basically
"un"spools the turbo)
The blowoff valve will "blowoff" this pressure buildup either back into the
intake path BEFORE the turbo but AFTER the Mass Airflow sensor (this is how
the stock WRX blowoff valve does it) or vent it to atmosphere.
Unless it came that way stock, a blowoff valve bumps you to Street Mod.
Ed
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