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Discussion Starter · #1 ·
I have just put a bigger turbo .What i am noticing is that it sounds like the bov is opening up and releasing pressure at part throttle. It didnt before when it was vented to atmoshere. Started yesterday when driving it started to have idling problems. I looked at the bov and it seems to stay open at idle sometimes.If i pulled of the vacuum line it closes and the piston seems free if you push on it. So i connected it back to the intake pipe and know i here it opening to early. This is a stock unit.Could there be a internal leak causing it to stay open??
 

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I love Cin
91 Turbo MR2
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The OEM valve is a BY-PASS VALVE, not a BLOW OFF VALVE.
As long as you have the AFM (Air flow meter) you can not safely vent the OEM valve.

Under non boosted conditions the OEM valve is OPEN to allow air flow around the turbo (hence by-passing it) to give you better fuel efficiency and throttle repsonse. If you have the OEM valve vented you are letting in unmetered, UNFILTERED air into your engine.

You will run lean (very) at idle and rich (very) at "blow off"

You can not set up the OEM valve incorrectly and expect it to work correctly.
 

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Discussion Starter · #5 ·
The valve is mounted correctly. Just wondering if it is normal for the valve to be open at idle?? Is it normal for the valve to open under part throttle?? Or do i have an internal leak in the valve causing it to open to soon???
 

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I love Cin
91 Turbo MR2
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I said "set up" correctly, not mounted correctly.

Did you read my post???
You just asked again "normal for the valve to be open at idle??
And I had said above, "Under non boosted conditions the OEM valve is OPEN"

It opens to allow air to BY PASS THE TURBO when you are not seeing positive presure (boost).

If you have the AFM in place, you can not safely vent the OEM valve to atmosphere.
 

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Discussion Starter · #8 ·
The problem is under boosting conditions the valve is opening and it should not. I just checked it and the valve is leaking. The valve is set up and mounted like it should. That was what i was asking. Not if it opens under no boost.
 

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I love Cin
91 Turbo MR2
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Unless the OEM valve is broken, there is no way it could leak under boost ~ no matter how much boost you put at it.

Do you have the vac lines going to the valve in the original orientation? .... with the VTV in place (facing the correct direction)?
The VTV is the little thing that looks like a filter on the bottom vac line.
That has to be there for proper function.

Here is a photo of mine:
 

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Discussion Starter · #10 ·
That looks awsome. Very clean. Which way shoul the vsv face is the dark coloured section to the valve or away fom the valve?? Cant tell on photo?
 

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I love Cin
91 Turbo MR2
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Here is an old writeup that Billwot used to post. Reference to "check valve" means the VTV (It isn't a true check valve).

"The large round area at the top is a diaphragm. The area on the top of the diaphragm is larger than the area under the diaphragm. Now note there is hose directly from the manifold to the top (large area) of the diaphragm, and another hose tee's off that goes through a check valve to the underside (small area) of the diaphragm. When there is pressure (boost) in the manifold, there is equal pressure on both sides of the diaphragm, but since force=pressureXarea, the greater force on the top holds the valve closed. In fact, the higher the boost, the more tightly the valve is held closed.

Now as soon as you lift, and pressure starts to drop in the manifold, air immediately escapes from the top of the diaphragm, but the check valve restricts it from escaping on the bottom, and the pressure on the bottom quickly exceeds the pressure on the top, and the valve snaps open. If you reverse or eliminate the check valve (VTV) then you can't trap pressure under the diaphragm, and the valve cannot respond as quickly.

Conversely, the check valve insures that when there is a vacuum condition, more vacuum will be applied to the top of the diaphragm, and it will open and be in bypass mode.


The diaphragm section of the valve is connected to a spool in the main section of the valve. That spool opens and closes the connection between the crossover pipe and the intake air pipe. When the diaphragm is pushed (or pulled) to the top, the valve is open, and when it is pushed to the bottom, it is held closed.

There is just a light spring on the spool in the main body. Its only function is to return the valve to its normally closed condition when the engine is not running."

Here ya go (mid-way down the page):
http://www.mr2-tech.com/bgb/mechanical/volume1/turbocharger_system/4.htm

If you want to know how the OEM BPV works see here:
http://www.jekylhyderacing.com/bov.htm
 

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Discussion Starter · #14 ·
Has anyone ever tryed to blow through the vtv valve, I can only blow through one way and according to manual you should be able to blow through both ways. One way easily and the other way with some ristriction???
 
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