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

[Djdawson2 at aol.com]

In a message dated 1/11/2006 6:16:03 PM Mountain Standard Time,  
tedebearp at yahoo.com writes:

dave,

are you sure that's how it works on the  UrS4/S6?
 
Yes... if you think about it, it is the only way it can work.



i agree with your description of the configuration, but
note  that the WGFV is plumbed to the lower chamber of  the
wastegate.
 
Yes... it is plumbed to the bottom of the WG, under the diaphragm.  If  boost 
is applied to the bottom of the diaphragm, it helps to overpower the  
spring... meaning less boost is allowed than if you were running a spring  alone.  If 
vacuum is applied to the bottom of the diaphragm, it helps to  assist the 
spring, meaning more boost is allowed than if you were running a  spring alone.
 



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.
 
Exactly.
 

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.  
 
Well, not exactly.  If the ECU wants more boost, there is only one  way it 
can do it... and that is by "strengthening" the spring.  This can  only be 
accomplished by introducing a vacuum into the chamber in the  WG.
 
If the WGFV is unplugged, you're right... full boost will go to the WG,  and 
as a result, your max boost allowed will be very low... well below the 14 or  
15psi you can get with just the spring.
HTH,
Dave