I was walking down the road the other day when a wrx was at a stop light. He/she took off quite rapidly and as they engaged the clutch you could hear a phhhhhhssssssssssssssst sound...like the clutch was air pressure...has anyone heard/seen this? What kind of clutch was he/she running? More curious than anything else.

B

wow..

 

It's a Blow Off Valve (BOV)

 

the sound you hear is the pressure that was built up with the turbo being vented out to the atmosphere has nothing to do with the clutch other then he has to depress the clutch to shift which then the BOV vents.

Interesting....it coincided with the clutch so I figured it had something to do with it. now I know

Interesting....it coincided with the clutch so I figured it had something to do with it. now I know

 

some people think it's not needed since all that air was metered air after the mass airflow sensor