ok, SO. how big can these valves come in?? When i say "big" I mean how big of an opening can you get them in??

and for the record, the one i installed on a procharged mustang, SNAPS shut instantly under hard throttle.

 

The boost in the vacuum line that comes from the manifold should push the valve shut faster than what it will shut by itself when vacuum goes to zero. You have to remember that there is both positive and negative pressure that act on that valve to open and close it.

 

There can be no pressure in the intake system anywhere, until the BOV is actually shut. spring pressure achieves that, and when shut, boost assists spring pressure to keep it shut until the throttle is closed.

 

Thats not true. I can make boost when my BPV is not all the way closed. It won't be as much as full potential, but I can make boost. However, that length of time that I am making and building boost when the BPV is slightly open (on its way closed) is a very short period since the boost in the line will assist in closing the valve (faster than it could by itself).

 

I'm bringing this back to the top because I'm wondering if you can change the spring pressure in the proflo bypass valve to start building boost sooner at less throttle.

 

That would be nice. There was also another thread on here about possibly putting something like a wastegate in line and setting it to open at x- amount of boost and just swapping to smaller blower pulley to get boost sooner down low. Guess that thread died???

 

I understand from a machanical point of view that one would assume that boost can't be made untill the bypass valve closes but I'm thinking in the real world the supercharger is pushing enough volume of air to still create some boost before the valve has time to fully close which would assist it in closing even quicker. I bought a new procharger race valve and noticed the thing doesn't snap shut quite as quickly as I expected when I tested just by pulling vaccume on it. Without the fitting for the vaccume line screwed into the top of the valve you can push the valve open and it will close a good bit quicker. My thinking is that the spring is having to suck air through the vaccume line to close the valve. That line is pretty small and restricts the air going into the valve making it take longer to close when you just test it by pulling vaccume on it and releasing it. I did the test with a hand held vaccume pump that you pump up and turn a screw to let air back into the vaccume line/valve, noticed how slowly it closed and unscrewed the fitting and pushed the valve open by hand and it closed quicker leading me to the conclusion that nothing was machanically wrong and the little vaccume line restricted the air going into the valve causing it to close slower. I don't think this will be an issue when the blower is trying to build boost at wide open throttle. I have a feeling the volume of air that is going into the system will start to build a little boost assisting the valve in closing rather than the vaccume line causing a restriction in the air entering like in the test I did.

Another thing I noticed is that the factory ATI bypass valve that comes with the system didn't even completely seal off when closed. I remember noticing this and trying to get it to seal better. I'm not sure what I did if anything but I remember messing with it to try to get it to seal better. I know I never could figure out why I was seeing 11psi when it was supposed to make 8psi and ii expected more like 7ish with a full exhaust. Maybe whatever I did to the factory bypass made it seal better. Its been so long ago I don't remember but I know the thing would not have sealed completely the way it was. You could see a pretty good gap between the blade on either side when it was "closed" either way, I was reading 11psi at redline and the #7 didn't last long...