Quick question. I saw a C6 Z06 over the weekend. It had a ECS supercharger kit. When the owner started the car it sounded like the BOV vented right away.
I have a very basic understanding of superchargers and was wondering what causes the BOV to vent right after starting.
Mabe it wasnt the BOV but it sounded like this whoosh @ 00:35 sec marker just after starting with no throttle.

 

The motor already was on in the beginning of the video, the person is revving the motor and because superchargers build boost based upon revs (where as turbochargers don't really build much boost in neutral because you need load on the engine) they need to release unused boost using a blow off valve or recirculation valve.

 

Sorry. To clarify the video is just an example of the sound I heard.
I do understand the function of a BOV but is there any reason why it would go off right after starting a car?
I guess it boils down to; Is there any unused boost right after ignition?
Because I heard the whoosh sound right after the guy started the car.

 

the BOV is what relieves pressure before the TB in order to not allow air back through the compressor (more important to a turbo here). On a supercharged car the pressure builds up as soon as the car is turned on vs a turbo needing to spool up. The other reason (and the reason SC guys use them) is so you dont blow out couplings when lettign go of the throttle.

well anyway, my bad. your question was why at startup his BOV activated, I assume it is because at startup his idle peaked at 2k rpms then fell down sharply thus releasing the plunger. so yes with a SC you may experience a boost spike at startup (especially on the LSx family of motors like in the video)

 

I believe you are hearing the supercharger itself. They make a high-pitched whine during operation.

Centrifugal supercharges don't create a lot of boost at idle (very similar to turbochargers, except driven by belt rather than turbine), so it's extremely unlikely you are hearing the blow-off valve over the sound of the engine & supercharger whine.

 

That makes sense.

The sound definately was not the whine of a supercharger. It was loud and sounded just like the sound in the video. I am 80% sure it was a BOV.
Could it be the sound of air filling the intercooler and pipes? Just a wild guess.

 

The traditional term for that device is called a wastegate.

 

Wastegate is on the exhaust side to prevent boost from building.

Blow off/recirculation is on the intake side to relieve already pressurized air.

 

OK, thanks for clarifying. As I understood it, they served the same function.