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

[Theodore Chen]

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.  

--- Djdawson2 at aol.com wrote:

> FWIW...
> The WGFV is basically a switch used to control the boost level at which the  
> WG will open.  It is also used to "increase" or "decrease"  the  strength of 
> the WG spring when required.
>  
> There are 3 ports on the WGFV.  1 of the ports goes to the  wastegate, and 
> basically is the means by which the ECU's desires are  communicated to the
> WG.  
> The other 2 ports provide the ECU the mechanical  means to either
> "strengthen" 
> or "weaken" the wastegate spring.  1 of those  2 ports goes to vacuum, found 
> at the turbo inlet.  The other 1 goes to  boost, found on the scroll of the 
> turbo's compressor housing.
>  
> If the ECU decides that all conditions are good for high boost operation,  
> the WGFV allows the vacuum source to pass through it to the WG, and this  
> effectively increases the WG's ability to remain closed.  Net result... the 
> WG 
> remains closed to a higher boost level than would be attainable with the 
> spring 
> alone.
>  
> If the ECU decides that conditions are not good for high boost operation,  
> the WGFV begins to cycle the boost port open, allowing boost to pass through
> it  
> to the WG, and this effectively decreases the WG's ability to remain  closed.
> 
>  Net result... the WG remains closed to a lower boost level than  would be 
> attainable with the spring alone.
>  
> If you take the ECU out of the picture by removing the WGFV, or  
> disconnecting the line to the WG, you will find that the stock WG spring will
>  allow about 
> 14-15psi of boost.  If you are running a header, you will  discover that a 
> stock WG spring is capable of holding the WG shut up to 25-28psi  of boost.  
> This can only be due to the fact that the exhaust restriction,  and therefore
> the 
> pressure built up between the cylinder head and the  turbine, is greatly 
> reduced.
>  
> Hope that helps,
> Dave
> 


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com