[s-cars] By-pass valves

[djdawson2 at aol.com]

 Mixing terms... and what you're saying isn't really accurate.

The valve, is normally closed.  Apply a vacuum and it opens.  Apply boost and it remains closed.  The signal comes from the intake manifold.  The intake manifold in a naturally aspirated engine is always in some state of vacuum.  This means that if you are not making any boost, there will be a vacuum in the intake... inclining the BPV towards opening.

Positive manifold pressure will NOT  "assist to force or blow the valve open when vacuum is applied to the control port" because those 2 things can't ever happen at the same time.  If there is pressure in the intake, there is pressure forcing the BPV to remain closed.  When there is vacuum in the intake, there is vacuum at the BPV opening it up.  Furthermore, boost hits the *side* of the piston (Forge) or diaphragm (Bosch)... never able to assist in opening the valve, unless you have it improperly installed.

If as stock BPV is installed backwards, you will blow the diaphragm in short order... it's just rubber, and it won't last long fighting 20+ psi.

The BPV's purpose is to alleviate pressure stall in the intake plumbing (and therefore the turbo) when the throttle closes.

Anyway....

 

 

-----Original Message-----
From: Ben Swann <benswann at verizon.net>
To: esanborn at gmail.com; dgraber460 at aol.com
Cc: 'Quattro List' <quattro at audifans.com>; s-car-list at audifans.com
Sent: Wed, Aug 11, 2010 6:51 pm
Subject: Re: [s-cars] By-pass valves


No, just the opposite.  The Bypass valve is normally closed.  The control port 

is vacuum

actuated and tends to open the valve.  Positive manifold pressure will assist to 

force

or blow the valve open when vacuum is applied to the control port.  This happens 

only

when the throttle valve snaps shut while engine is under positive pressure - 

like

between shifts.



So the mityvac test is not necessarily going to tell you if the valve is opening

properly and some valves have beefier springs for higher boost pressure.



Also, if the valve is installed backwards then it may not open or flutter when 

opening,

or open when it should not open.  Funny thing is the way most valve are 

oriented, the

correct way does not look correct.  You  might want to verify that the direction 

of the

valve is correct.



See: http://www.gtquattro.com/Bypass-Valve.html that has a picture of how the 

valve is

connected/oriented.



Ben



[Date: Wed, 11 Aug 2010 17:56:43 -0400

From: Eric Sanborn <esanborn at gmail.com>

Subject: Re: By-pass valves

To: dgraber460 at aol.com

Cc: s-car-list at audifans.com, quattro at audifans.com

Message-ID:

    <AANLkTin-vkgjJaotOtbbX3ToE1Ab-yLvLzkJ2293n-xq at mail.gmail.com>

Content-Type: text/plain; charset=ISO-8859-1



I might be misunderstanding what you were testing, but they should only open

during boost.



On Aug 11, 2010 5:12 PM, <dgraber460 at aol.com> wrote:



List-et-al;

I have been chasing a full throttle issue on my 3B'd URQ for a few months

now. The symptoms have been a flattening and lack of power under full

throttle. My boost gauge has always shown full boost at 19-20, and it throws

no codes. I started to notice the moaning (not whooshing) noise when off

throttle, which I had heard before and found to be an aluminum bypass valve

that needed cleaning.

Since it had been running an OEM Bosch plastic valve, I pulled the Forge

valve off the S-Car and cleaned it up and installed it. On the drive this AM

it seems to have cured the issue. Time will tell if total cure.

The question I have is that I tried to test all 3 valves that I have while

messing around last night. I have 2 plastic, and 1 Forge valve. I hooked up

a vacuum pump that pulls 14 lb hg to each valve individually and _none_ of

them would pull open. Then I used my little Mighty Vac hand pump and the

Forge valve would pull open and stay. Neither plastic OEM valve would open

with either test. Does this indicate both OEMs are toast?

I assume the vacuum pump did not have a check valve and therefore could not

"build" vacuum as the Mighty Vac did, thus letting the valves flutter but

not pull open. Sound reasoning?

Also - is there a recommended lubricant that keeps the aluminum valves

happy, and functional, or should they remain dry?



Dennis

Denver

]

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