Two vacuum lines on bypass valve ?

[stephenpen]

I just noticed my bypass valve has 2 different vacuum lines running to it. The lines coming from the top of the valve gets its vacuum from behind the throttle bodies. The other line loops to a fitting threaded in the upper intercooler end tank.
Does anyone know why this is. My bypass valve on my car only uses one line.

 

[stecka]

supercharged?

 

[kinger]

If your using the MPI 2 way BOV its a nice piece and might explain the two hoses.

It supposedly blows off boost at light loads vs running full boost cruising as a one way valve does (like my vortec)

I was thinking of switching to the 2 way once I had some feedback on it.

 

[stephenpen]

I'm pretty sure my bypass valve is a Vortec. I still don't understand why it uses 2 vacuum lines.
My big red procharger bypass valve stays open until you reduce vacuum by pressing the throttle. Full vacuum its stays wide open and bleeds off the boost.

I read something about a bypass valve that you can adjust to lower the amount of boost the engine sees. Could this be one of those units.

Kinger
Your Vortec only has one vacuum line ?

 

[kinger]

Well my vortech has one line and then a cone shaped filter on the other side. There is a way to plumb the vortech so that you can reduce the boost by half of what your pullied for by removing that filter cone thing and plumbing in boost to the valve (ie to center the valve and if your making 10 psi 5 psi will bleed off and 5 will make it to the engine.

So probably not what is happening but take a picture of it its worth 1000 words.

 

[stephenpen]

Here are a pictures.

 

[kinger]

That spot down low where there is a nipple screwed in I just have a filter there, its a bronze cone looking thing. Looks to me like someone was playing with adjusting the boost.

The line that goes on the top nipple is vacumn right? So basically what your doing is running 10 psi on the bottom and 10 psi on the top (under load) and your going to net 5 psi or half of what your running.

 

[spddmon]

that is a way to make that valve a differential valve similar to the mpi bov

 

[stephenpen]

I just got off the phone with MPI and they say thats the way its supposed to be. One line goes before the throttle bodies and one after the throttle bodies.

 

[kinger]

??? I need to understand this. I have my line from behind the throttle bodies going to the top of the valve only.

 

[stephenpen]

??? I need to understand this. I have my line from behind the throttle bodies going to the top of the valve only.

Did you figure out why ours are different.

 

[kinger]

No I haven't this is the way Ulmer racing set it up for me.

 

[Srxspec]

That is just a secondary way to hook it up and use it as a "differential" valve instead of just a bypass valve (which only opens under vacuum). The way it is setup in the pictures it will cut the boost in 1/2 of what the pulleys are (which I think is adjustable by adjusting the screw in the valve to change how much boost is actually being blown off). The way the picture shows it setup will help with fuel mileage, etc. I haven't ever had a chance to test that setup myself, but have had a customer that did it and said it worked excellent.

 

[kinger]

So if your pullied for 10-11 psi the way I have it hooked (bypass valve) I will see a full 10-11 psi. The way he has it hooked up he will have to manually adjust the spring and see a little less then 10-11 psi because he will always be blowing off some boost, which is good at light load for mpg but bad for WOT when you want a full 10PSI.

This right?

 

[stephenpen]

So if I unhook the hose coming from the intercooler to the bypass valve I should see more boost.