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Discussion Starter #1
Why is it our BOV's stock are between the accordion hose and the throttle body, but all aftermarket ones go on the IC piping right before the throttle body?

I understand the vaccuum line on top tells it when to blow off, so when it blows off the air goes into the throttle body? Relieving the air from the accordion hose?

As for the aftermarket ones that mount on the IC piping before the throttle body, when they blow off where does the air go?

How is it that the stock one and aftermarket ones do the same job but mount in totally different locations with totally different pressures going to them?
 

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I once read that the stocker isnt a real BOV but is actually a bypass valve and allows air to bypass the turbo for better fuel economy. It also releases the pressure back into the intake when you shift/let off hard.

If I'm wrong someone please correct me.
 

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Discussion Starter #4
DevinWolfe said:
I once read that the stocker isnt a real BOV but is actually a bypass valve and allows air to bypass the turbo for better fuel economy. It also releases the pressure back into the intake when you shift/let off hard.

If I'm wrong someone please correct me.
yes the stock one is a bypass valve since it does not vent to atmosphere.

It confuses me that the stock valve mounts before turbo/after throttle body (I mean where the hoses connected to it go) and aftermarket ones mount after turbo/before thottle body.
 

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umm, the stock blow off valve IS mounted before the throttle body. It recirculates pressurized air from before the throttle body (the hose connecting it to the 3000 pipe) TO the accordian hose, not the other way around.
 

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This all seems pretty correct. The thing is i assume we all know blow off and by pass valves exist to prevent surge to the turbo. Pressure surge being a gust of air that slams against a newly closed throttle body butterfly and begins to head backwards toward the turbo endangering its lifespan. When a by pass valve opens, it releases measured air back to a point in the system before the turbo but after the AFM. Therefor, no air that has been accounted for already by the computer has escaped the mixture. However, when a blow off valve vents to atmosphere it is letting go of air that the AFM thinks is still there. Consequently, the computer allows for more fuel, not knowing air has escaped and you end up running rich considering the air has been let go after it was measured by the AFM. Also, just as they have mentioned before both types of valves are mounted before the throttle body, the only difference is one vents to atmosphere and the other vents to the other side of the turbo in your intake system.
 

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The stock bov is actually a recirculating valve. When you let off the throttle it recirculates the pressurized air back into the intake just before the turbo - the Z32TT does this too. The idea is that you've got all this pressurized air already built up, why waste it by venting it into the atmosphere?

As for the bov that vents to the atmosphere, they can be almost anywhere between the turbo and the tb, including the ic.
 

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Discussion Starter #11
So a leaking stock BOV can 'cause a idle issue and dying when giving it some boost and abruptly jumping off of the gas and clutching? Someone suggested that since it recirculates if it did leak it would just put the leaked air back into the intake and not cause any issues.
 

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sg02 said:
So a leaking stock BOV can 'cause a idle issue and dying when giving it some boost and abruptly jumping off of the gas and clutching? Someone suggested that since it recirculates if it did leak it would just put the leaked air back into the intake and not cause any issues.
If the stock BOV was stuck completely open, your car would still run perfect (though a little slower).
 

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Discussion Starter #13
Racefiend said:
If the stock BOV was stuck completely open, your car would still run perfect (though a little slower).
So a leaky bov that recirculates is no problem? Well hum I was hoping that was my issue, still gotta hunt it down. No bother.
 
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