stupid question about bypass valves...

[Ritter]

so, my thought process makes me believe that at idle a bypass valve(lets say a vortech mondo) is open, allowing air to bypass so the car will not make any boost. does that sound right? seeing as the car has 18-20lbs of vacuum at idle, shouldnt the bypass remain open until vacuum goes away? anyway, that is my stupid question for now, please post what you know. i searched and didnt find squat. thanks guys!!

[speedytang]

The valve stays open till boost so it does not stop from making boost. When you make boost the valve closes then opens as soon as a vacuum condition to allow the boost to be released into the intake side of the blower.

[BLOWNBY]

The mondo is adjustable as to how much vacuum it will require to open however.

Either way at idle even if the bypass is closed the car will still be in a vacuum.

But what has been stated above is true... In general at vacuum the bypass is open and under hard load (boost) the bypass is closed!

[superchrgd331]

now i have question also, how much should you adjust that screw on the valve, i have a mondo, and the screw is pretty far out (loose). how far should i screw it in to adjsut the valve, the car makes 20 psi. with it so far out it does not seem to hold closed for that long and when it is still under load it will blow off. any help will be awesome.

[BLOWNBY]

Typically they are pretty much all the way out. It shouldn't open under boost. As they take like 3-4 of vacumm just to open as is. As you tighten the screw it takes more vacum to open.

You could try turning it in a turn or two and see if it helps, but it shouldn't matter under boost!

[RSNovi]

If the valve is working properly, it will never open under boost. As previously mentioned, you can adjust how much vacuum it takes to open. The adjustment doesn't adjust how much boost it holds.

The only time I ever tried adjusting the valve was when I was trying to see if I could minimize blowing off boost when letting off the gas at my shift point. Never concluded if any adjustment ever helped. I am able to not blow boost off by power shifting.

[Dave R]

So you would either have to run the bypass back to the intake tract or run a filter on it (non MAF systems) so when in vac, it doesn't suck in dirty air??
I have a mondo. If I idle at 15 inches, and adjust the valve to be closed at 15 inches, it'll not open until it reaches over 15 inches, correct? That would have it blow off to atmosphere only when letting off after a hard throttle run. Am I thinking right?
I'm just trying to understand why most run them back to the intake tract and I see renegade type setups run them to atmosphere. Sounds like a race tune setup.

Please explain.
Thanks
Dave