Re: K24 and boost - more on WGFV

[QSHIPQ@aol.com]

In a message dated 11/24/99 4:09:51 AM Central Standard Time, 
isham-research.freeserve.co.uk@pop.freeserve.net writes:

> > WG springs on 10vt.  M. Peterson hasn't presented this concept quite 
right.
>  > The WG frequency valve either does nothing, or adds boost pressure above
>  > spring pressure to the top of the WG.
>  
>  Even that isn't quite right.  The WGFV switches between what passes for
>  vacuum on the car (from the turbo inlet) and 'boost' - which may come
>  from the unthrottled boost chamber cast in the inlet manifold or from
>  the inlet manifold itself (throttled) depending on the exact level of
>  the engine.  Later engines use throttled boost to the WGFV - I haven't
>  yet settled on an explanation for Audi's change.

Not quite right either Phil.  The WGFV duty cycle is to regulate the amount 
of boost that goes to the top of the WG.  Since the WGFV applies a percentage 
of manifold boost to the top of the WG, that means there will be some excess, 
that needs to go to a non boosted inlet (otherwise you have a boost feed and 
a boost return = boom).  When there is no WGFV operation, the manifold feed 
line is blocked.  When the WGFV operates, at 100% DC, the return (Turbo 
Inlet) line is blocked.  You can verify this by applying voltage to the WGFV 
(thanks Dave L).  So, we can then say that at 100% DC, top of WG boost = 
Manifold boost.  Saying that the WGFV switches between vacuum and boost is 
really not correct.  When it's off, whatever vacuum is in the TI goes to the 
WG.  It really isn't that significant, if it was, you would see a longer 
spool up time for the turbo between 0 vacuum and boost.  A better way of 
thinking of the WGFV is similar to a FPRegulator.  An FPR is used to regulate 
the amount of postitive fuel pressure, but the excess needs to go somewhere.  
Same principal to the WGFV.  

>  
>  Anyway, when it's applying 'vacuum' - the force tends to lift the
>  wastegate.  On the MAC12D and MAC14, the WGFV operates whenever the
>  WoT switch is closed, although the duty cycle varies considerably with
>  the actual boost level.  A diode light (I use a design that Orin came
>  up with) is a 100% method of testing WoT function.

Not really true either.  I suppose you could argue there is a "tendency" to 
lift the WG.  However, those with let's say Charlie spring mods (free ad 
charlie:), will have no WGFV operation (always vacuum applied), but get more 
boost, and has a lower tendency to lift the WG.  On the MAC11> the WGFV 
operates whenever the WOT is closed.  The diode light is NOT a 100% method of 
testing WOT function.  3 ohms of resistance is enough to fool the computer 
regarding WOT (a long standing Ned Ritchie tech tip), but can still activate 
the diode light.  The only 100% method of testing WOT function is to use an 
ohm meter on the switch.

>  
>  Of equal importance - does the ECU actually _abandon_ the WGFV (leave it
>  switched to vacuum) at any point?  This phenomenon is common close to
>  redline on shimmed wastegates - it's a good indicator of too much shim.

All the time.  Try this, hook up a LED to the WGFV terminals, and route it 
into your dash.  You can fine tune any chip/spring mod to YOUR car by 
watching the LED, it should light as much as possible.  When it doesn't, that 
means you have too stiff an effective spring pressure for the tables in your 
chip.  When it doesn't light at all, you either have a faulty WOT switch, or 
you put in too stiff a spring (or you have some other boost limiting 
problem).  Most stage II (chip not resistor) mods do best with a 1.8bar 
spring IME.

>  What is surprising, the first time you see it, is the rate at which the
>  valve runs - several Hz.  With a very lightweight mechanical pressure
>  gauge in the line from the WGFV to the top of the wastegate, the
>  indicator needle just becomes a blur.  I had expected a quite crude
>  on/off switch.

The duty cycle of the WGFV operates between 5 and 95%DC to ground.  This 
applies to both the 10vt and the 20vt.  You can get a better measure of the 
DC by using a dwell meter (DC = 90% of 4cyl dwell), analogs are easier to 
watch than digital, since analogs average in a way that the eye can follow.

HTH

Scott Justusson
QSHIPQ Performance Tuning
QSHIPQ@aol.com
'87 5ktqwRS2 -10vt 
'84 RS2URQ -20vt
'87 4Runner turbo