[s-cars] While we are on the subject of WGFVs...

[Tom Mullane]

Teddy is correct.  Unplugged, or without voltage from the ECU, the
WGFV allows boost through to the WG, opening it.  When voltage is
applied, the valve opens the third port, allowing boost to both the WG
and into the intake boot.  This bleeds enough pressure off so that the
WG does not open.

In the past, we tried to relocate a WGFV using a large diameter vacuum
hose to move it away from the intake boot a few inches.  The distance
was too great to properly bleed boost, and the WG would open
prematurely.

Tom

Date: Wed, 11 Jan 2006 17:25:27 -0800 (PST)
From: Theodore Chen <tedebearp at yahoo.com>
Subject: Re: [s-cars] While we are on the subject of WGFVs...
To: Djdawson2 at aol.com, bob at chips-ur-s.com, s-car-list at audifans.com
Message-ID: <20060112012527.23226.qmail at web50603.mail.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1

oops, that last one got away from me early.

dave,

are you sure that's how it works on the UrS4/S6?

i agree with your description of the configuration, but
note that the WGFV is plumbed to the lower chamber of the
wastegate.

the WGFV has three ports on it.  the left port goes to the
wastegate.  the right port goes to the turbo intake.  the
bottom port goes to the turbo output.  normally, the
bottom port is connected to the left port and air can pass
freely.  normally, the bottom port is not connected to the
right port and air cannot pass between these two ports.
when the WGFV is actuated, all three ports are connected
to each other.  i verified this by applying 12v to the WGFV
and blowing through each of the ports.

the way the wastegate is plumbed on the UrS4 is that boost
is used to open the wastegate.  if the ECU wants more boost,
the ECU implements this by actuating the WGFV, thereby bleeding
boost off into the intake.  if the ECU never actuates the
WGFV, all the boost from the turbo goes to the wastegate
and the wastegate will open at the default pressure.

what you described would make sense if the WGFV were plumbed
into the upper chamber of the wastegate, but it's not.  that's
why we have a nipple on top of the wategate with nothing
connected to it.  i think what you described is how the
audi turbo engines used to be.

references i've seen say that the stock wastegate spring
is good for about 6 psi, and that's consistent with what
i'm seeing during times of low boost.  i have an indicated
1.2 bar on the digital pressure gauge, and with a correction
factor of 1.2 (i have a 3 bar pressure transducer vs. the
stock 2.5 bar pressure transducer), that works out to about
6 psi of boost.

i'm relying on scott mockry's page:
http://www.sjmautotechnik.com/trouble_shooting/20vwgcnt.html

-teddy