What vacuum mods to make?

rustfarmer

New Member
Jul 20, 2009
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Centerville, TN
Just about to finish up 7M GTE rebuild with some mods. After market intercooler and pipes, the "3000" replacement pipe does not have bung for hose that goes to the vacuum switched 1/2" hose that I don't know the function of. Does someone have a diagram of all the vacuum lines and what is needed and what can be safely deleted? Thanks. (FWI, I am using the replacement turbo elbow and full 3" exhaust from Driftmotion)
 

Bmettie

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Apr 27, 2010
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That thing you don't know the function of is the factory bypass valve (blow off valve) and you should have one, factory or aftermarket.
 

rustfarmer

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Jul 20, 2009
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Centerville, TN
Perhaps I was less than clear, since I don't know what the hose in question is for. It is large (1/2' id) and runs from the 3000 pipe through a vacuum operated valve then to the accordion hose. I don't see it in the routing diagrams you so kindly provided.
 

Enraged

A HG job took HOW long??
Mar 30, 2005
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Victoria, BC, Canada
That's the factory bypass valve, or BOV. It will have two big hoses, and You need it, or an aftermarket alternative.

This thing, two big hoses, 1 small vacuum line:
p2059713_1.jpg
 

supraguy@aol

Well-Known Member
Dec 30, 2005
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Atlanta
Be aware that if you vent the aftermarket blowoff valve to the atmosphere(rather than recirculating it), you will
generally encounter stumbling and stalling issues after letting off boost. That is, if you're on the stock MAF.
 

IndigoMKII

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May 9, 2011
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supraguy@aol;2059828 said:
Be aware that if you vent the aftermarket blowoff valve to the atmosphere(rather than recirculating it), you will
generally encounter stumbling and stalling issues after letting off boost. That is, if you're on the stock MAF.

Only if his VTV by the throttle body isn't working correctly. The throttle shouldn't slam closed but most overlook it.
 

TurboStreetCar

Formerly Nosechunks
Feb 25, 2006
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Long Island, Ny
Even with an operating throttle dash pot, it will still stumble and falter. It's not a matter of the throttle closing too quickly it's a matter of the air that has been drawn threw the AFM has already been accounted for, and fuel has been added for that air. A vented BOV allows this metered air to escape but the fuel is still added.

This results in a ton of fuel being thrown into the motor with almost zero air to burn it.
 

rustfarmer

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Jul 20, 2009
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Centerville, TN
Nosechunks;2060401 said:
Even with an operating throttle dash pot, it will still stumble and falter. It's not a matter of the throttle closing too quickly it's a matter of the air that has been drawn threw the AFM has already been accounted for, and fuel has been added for that air. A vented BOV allows this metered air to escape but the fuel is still added.

This results in a ton of fuel being thrown into the motor with almost zero air to burn it.
Thanks for this info. Makes good sense, so if running a modified intercooler pipe and the fancy (and wrong, apparently) BOV, is there a simple work around? If I want to use the new BOV is there a easy way to dump the air back into the intake?
 

Janch

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Jul 23, 2012
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Riga
im sure you could attach the hose to BOV and recirculate it back into the intake. if you like that chu chuuu sound you can use high flow air filter, with even better aluminium intake pipe that will resonate the sound and you'll be able to hear it pretty loud. some bows even have option recirculated or vented in atmosphere.
 

IndigoMKII

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May 9, 2011
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rustfarmer;2060419 said:
Thanks for this info. Makes good sense, so if running a modified intercooler pipe and the fancy (and wrong, apparently) BOV, is there a simple work around? If I want to use the new BOV is there a easy way to dump the air back into the intake?

You can buy a recirculating kit online.
 

TurboStreetCar

Formerly Nosechunks
Feb 25, 2006
2,776
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Long Island, Ny
Is your car a stick? It's not likely to stall between gears because the speed of the car and the solid connection of the clutch keeps it turning.

However on an automatic or in slower speed maneuvers it can release enough air to cause stumbling/stalling. If the motor stalls you use power steering.