I have a good working knowlege of how forced induction works, however something boggles me.....
I have also owned a few Turbo cars....like a Subie. My work vehicle is also turbocharged.

What is with the blow-off valve noise?....You know the pooooossssshhhhhtt sound coming from most of these after market turbo chargers. I realize it is excess boost being "blown-off".....but is all that noise needed? I know it must be music to the ears of a car enthusiast......including me, but ONLY if it is purely functional. I have a sneaking suspicion that it is sort of engineered into the design to give it a trendy head turning sound. That is to say....they could make it silent if they wanted to (like many cars with factory turbochargers) and yes blow off all the extra pounds of boost just the same.

The turbo charger in my Subaru has a "waste gate" that would bleed off excess pressure created from boost, and did so totally silent. Does a blow-off valve replace the wastegate?.....or is it the same thing with two different names.

Why do I need to advertise to cars all around me that my car has a turbocharger?

 

There are two ways to vent a blow-off-valve:

1.) vent to atmosphere

2.) recirculatory - pressure is recirculated back into the intake.

Vent-to-atmosphere is usually the loud "pshhhh" you hear but you can get a similar sound with a recirculatory valve and open air element (K&N intake) as well.

The noise is there to turn heads. It's not a sign of a really fast car or a car with lots of boost. It's just an attention grabber.

The BOV and wastegate are two different peices. A BOV is for bleeding off excess pressure in the intake (post-compression).

The wastegate on the other hand is there to let exhaust bypass the turbine. The purpose of this is to also reduce boost pressure. It basically keeps the turbo from spinning too quickly at high engine rpms and causing an overboost situation.

 

Wombie,

I think Gyro was saying that both the "blow-off valve" and wastegate are bleed valves and the wastegate can be made silent so why can't the blow-off valve. You answered this with #2.

 

yeah, the ricer BOVs are the only ones that are super loud, and are vented to atmosphere only for that reason.

you can pipe it back into the induction system, save some energy, and cut the noise down.