Ok first some background. I used to own a Z24, and I was gonna turbo that, so I researched turbos, and didn't give S/C's a chance except Centrifugal, which is just like a turbo...but you knew that already. I know BOV's are designed to release the excess boost not taken in by the engine from the turbo. I'm still trying to figure out everything about how these S/Cers work, and I would think that when you release the petal that the turbines are still spinning creating some kind of boost, so what happens to the extra boost not taken in by the engine? I saw that video of the airflow, but couldn't understand it b/c there was no sound. So can someone please help me understand the WHOLE system?

I am aware of how the roots style s/c's work, I just dont know how the system works. Like I could take you through the whole Turbo system starting from the exhaust, or wherever, and that is what I'm looking for. Thanx

 

http://www.cobaltss.org/media/2.0-Ecotec.wmv

 

The video you are talking about I assume is the animation of the LSJ supercharger operation. There is no blow off valve. There is a bypass valve, which is how the intake air charge by-passes the compressor. The video distinctly shows how the by-pass operates equal and opposite to the throttle valve. Closed throttle, open bypass. Open throttle, closed bypass.

 

Well like I said there is no sound, and I dont really know what I'm looking at...

 

Well like I said there is no sound, and I dont really know what I'm looking at...

 

There is a bypass valve that allows fresh air to enter through the throttle body and bypass the superchargers rotors avoiding boost. The bypass valve is vacuum controlled (Via a solenoid) and operates inversely proportional to the throttle plate. While off throttle and in vacuum the bypass allows air to pass through and when the throttle is engaged as vacuum drops the bypass valve closes giving only a path through the supercharger rotors which will "blow" it into the intake manifold causing boost.

#1. Since the blower is attached to the engine by a belt and does not freewheel like a turbo the compressor does not technically "surge".

#2. Since the bypass valve opens inversely to the throttle, when the throttle is released the bypass valve then opens allowing airflow to the engine.

 

ahhh. i see...so the extra boost not taken in by the engine goes thru the bypass valve and is sucked in by the engine as it needs it?

 

Yes, I kind of misworded that part. The extra air goes through the bypass valve back to the supercharger inlet and is then used by the engine as needed. You have the right idea.

 

ok thanx.

 

No problem.

 

There is no excess boost. Inlet air bypasses the compressor, so it doens't boost anything. And you don't need sound, there really is nothing to hear.

 

True, it is not excess "boost" because it's not pressurized, but it is unused air which is recirculated.