amoosenamedhank

What method the air is compressed by should have no bearing in this situation.

I've been trying to think of ways to explain this better so here it goes.

The BOV sits a top the intercooler piping. During WOT situations, there are two points of pressure going against the BOV. One coming through the 'reference line' (vacuum line from the plenum) and the second is on the piston from the piping side. When these pressures are equalized on both sides, the piston is held closed.

When the throttle is closed at idle or deceleration, there is a discrepancy between the vacuum from the referenced line (from the intake manifold) and below from the piston. The manifold pressure being higher than the pressure below the piston. The piston will have the natural tendency to open. This is where your spring comes into play. You need to chose the appropriate spring/shim combo (or if your BOV has an adjustment screw) to allow the the piston to be held shut.

Right now, for those of you who have the incorrect adjustment with your BOV resulting in your BOV being open during vacuum... you are basically just allowing un-filtered air into your system. Not only does air escape there, it also enters there.

jvog

My bov is open when not in boost, if it was closed then at idle when the bov is closed the blower would be pushing air (not a lot, but air none the less) towards a closed throttle plate

amoosenamedhank

You always have atmosphere pressure... trust me, it should be closed. At idle your throttle plate is also not 100% closed, otherwise it would starve the engine of oxygen.

jvog

I know its not completely closed. My max flow bov is designed to open at 4 hg of vacuum. How would it not be open at idle?

amoosenamedhank

But that answers your question. The BOV can be closed at idle because the throttle plate is open.

You say designed to open at 4in/HG... What is it in the design that ditacts that? Either way, the spring is what is holding the valve closed during idle, PT and decel.

Kerns

I'm well aware of how the BOV will function on most turbo charged applications. However, if you go off of the chart our cars are around -19 to -21 hg at idle and we should be running the 9psi spring. However, for some odd reason on a supercharged car if you run a 9psi spring when you let off the the throttle, your BOV doesn't release the built up air like it is supposed to. It will barely open up at all. For supercharged applications you TIAL recommends going with their 3psi spring.

Edit: Also, the 50% throttle was basically just a reference for when my manifold pressure starts to overtake my piping pressure and allows my BOV to close. More accurately, it closes when I am around roughly 30% throttle.

Also, there was a huge discussion about this on the Corvette forums awhile back.
http://forums.corvetteforum.com/c5-f...ch-spring.html

jvog

Sorry, not the actual design of the bov. The spring in it is set up to open at 4in/HG. If the car has 20in/hg at idle...it will be open....

amoosenamedhank

Ok I give up.... I'm not going to keep running in circles here. If your cars are running well in this configuration... More power to you and best of luck.

Bman2000

i get what your saying hank....altho i do have a question...why is it that all the blow through set ups i have seen so far the BOV wistles at idle? that would mean that the bov is letting air out right? the only quiet sc set ups ive seen are draw through and have a bypass valve? just trying to understand better

Blk003GT

IM blow thru and mine dosent whistle its quiet