[kyle_c_21]

subject says it all. what is a blow off valve and what exactly does it do? thanks

[Vortex]

takes the boosted pressure from a turbo and releases it into the air to keep the manifold from blowing up.. its the high pitched air-release sound you hear between shifts on turbo cars...

[kyle_c_21]

ok, thanks.

[JUSTNLX]

A blow-off valve does release pressure in the intake track.

On a S/C, which has a positive drive (belt), it will release the pressure build up in the intake when the throttle is closed. This pressure build up has no where to go except back to the S/C. With the S/C positive drive, this can damage the vanes on the impeller. That is why you use a blow-off valve to release the pressure on a S/C.

With a turbo it is almost the same thing. A turbo is driven, in simpler terms, by the exhaust. They do not have the positive drive like S/C. As the pressure goes back on the impeller, it slows the impeller down. This creates “turbo lag” when the impeller has to come back up to speed when you reopen the throttle. A blow-off valve releases this pressure and allows the turbine to spin freely creating less “lag”. In high boost applications with a turbo it does the same thing as a S/C plus reduces lag.