A BPV attached to a supercharger system is open all the time venting off the excess air from the supercharger until the load is increased significantly (WOT) in which the vacuum reference line pushes on the diaphragm in the BPV thus closing it. When it is closed all 100% of the air from the supercharger is forced into the intake thus creating a positive pressure aka "boost".

Superchargers flow a set amount of air based on RPM alone. If you are cruising at 5000 rpm then the supercharger is pushing out XX amount of air. The reason a person can cruise at 5000 rpms and not be in boost on the highway is because the BPV bleeds off the excess air from the supercharger. Now while you are cruising at 5000 rpm you push the gas pedal down all of that air will then be forced into the intake as the BPV is forced closed and you will be at whatever boost you produce at 5000 rpms. It's not like a turbo system that only spins as fast as the exhaust gas pushes it. Superchargers spin the same speed based on rpm every single time hence the reason they don't need to "spool". It's instant boost as soon as the BPV shuts.

 

Thanks Jeff! That is a great explaination, I had no idea (clearly) that this system worked that way.
My understanding was that because it doesn't create boost until higher RPM anyways, there would be no need to purge boost that is literally non-existant anyways until high RPM. I guess I just have my head stuck trying to sort the reasoning out, perhaps I"m just thinking too hard about it.

Admittedly though I'm still confused on one big part:
How it acheives this unless it's dumping to atmosphere, if the Manifold pressure is what's connected to the BPV, then where does the purged boost pressure go? Is there a separate vent line that goes back into the Pre-supercharger (filter) that I am unaware of?

 

The vac source is a 1/8" reference line that attaches to the top of the BPV. There is a spring and internal diaphragm. With the car off the spring gently holds the valve closed. When the car is started the vacuum pulled from the engine puts a negative pressure on one side of the diaphragm which pulls the valve open (and then the excess supercharger air goes out that valve into the atmosphere. When the driver puts a heavy load on the engine (wot) the engine loses vacuum which then allows the spring to push the BPV closed and then all the supercharger air goes straight into the intake.

Recirculating the BPV doesn't change performance. It's only to reduce noise. It gets recirculated to the filter side of the supercharger on some car systems so all that recirculated air will just come out the air filter if there is more air produced than being sucked in. It won't force air into the supercharger (unless the air filter is 100% clogged).

A BOV works quite a bit different. It is closed while driving since the turbo isn't pushing a lot of extra air (spinning slowly with no load) but once the car is WOT the turbo starts building pressure and then the vacuum line reference will have a positive pressure thus holding the BOV closed against the pressure inside the intake tubing. Once the throttle is let off the pressure inside the intake piping is high and the pressure after the throttle body (which would be the vacuum source line to the top of the BOV) is low thus allowing the air to push open the BOV and bleed off excess pressure. So it doesn't just leak air all the time like a BPV.

 

hey man one question. by any chance you how to adjust the BPV from the vortech. I wanna adjust it at the point that it opens when it has heavy pressure on it.

 

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