manual boost controllers, and ECU functions

[QSHIPQ at aol.com]

In a message dated 2/1/01 5:24:21 AM Central Standard Time, 
isham-research.freeserve.co.uk at pop.freeserve.net writes:

> > in audis.  Wastegate cracking is specifically what's happening.  For more,
>  > get Maximum Boost from Corky Bell.   If you had a stepper motor from a 
> manual
>  > boost controller, you could use the stock spring or less with better 
> results.
>  
>  Yes, but there isn't much scope in such a system.  A really _noticable_
>  change requires a stiffer spring.

Disagree.  A really _noticeable_ change requires a boost controller.  The 
scope in the systems without the spring is the same.  The problem is that the 
WGFV can't add enough boost fast enough to overcome initial wastegate 
cracking.  This is what gives midrange torque.  A failure of the design of 
the WGFV, *not* the wastegate or the spring in it.

>  > No.  The reason a chipped ecu reaches boost sooner or later has 
*nothing* 
> to
>  > do with the turbo, a turbo can overboost within 3 seconds quite easily.
>  
>  Three seconds is an effing long time to be alongside an articulated
>  lorry on a country road waiting for the boost to arrive.  If a stiffer
>  spring shortens this by only half a second it's worth doing.

Basic misunderstanding of boost, and how it works.  To blow up a turbo, you 
hook up a line from the manifold to the top of the wastegate, stock spring.  
Putting a stiffer spring won't make it blow up sooner or later.  If the 
wastegate is closed the turbo can't ramp up any faster.  
.
>  
>  The WGFV loop runs at about 6Hz.  I agree that its scope is limited and
>  said so previously.

Try a stepper motor in a HKS or Greddy boost controller sometime Phil, it 
puts the audi loop in perspective.
>  
>  > IMO, you shouldn't blame the turbo for the crappy audi WGFV function.  
For
>  > purely boost function aftermarket controllers are better than audis.
>  
>  It depends what you want the WGFV to do.  Its design goals are to reduce
>  turbo lag by programmed overboost and fine tune output by eliminating
>  some manufacturing tolerances.  It's not intended as a major contributor
>  to the system.

A WGFV is designed to ADD boost pressure on top of baseline WG spring 
pressure given Charge Air temp, WOT, Atmospheric pressure, water temp and 
knock inputs.  It's major function is to provide a safety net in case any of 
the above inputs are out of range:  Baseline spring pressure prevails.  The 
problem with adding a stiffer spring is that when the WGFV shuts off, you 
have increased the risk of boom.  Bottom Line:  Boost controllers have become 
way more sophisticated than either of audis WGFV (the old top feed *AND* the 
still used 1991 edition bottom feeder).  In the case of the post 1991 turbos, 
the WGFV *IS* the major source of boost control (you don't need any spring to 
get boost).  And it fails more regularly than the pre 91 WGFV's.  Since 
circa1990, HKS (and since Greddy) have offered a phenomenally accurate and 
simple device called a stepper motor which don't fail, have dead nuts 
accuracy, and are inherently a better design at controlling boost.  I 
personally cringe every time I have to put one of those 3 pronged WGFV in 
turbo cars (which includes the 1..8T's).  You try a stepper motor, you have a 
hard time going "back".  Some folks are on their 4th WGFV on their S cars, 
that's 300USD thrown away on one big ole POS, IMO.

I don't agree at all with your understanding of boost, control or function 
Phil.  When you get the time, please take a ride in a car with a manual boost 
controller and post your thoughts.  Audi needs to do better here, cuz 
"better" has been around a long time now and proven it's worth.

Scott Justusson
'87 5ktqw 
'87 4Runner turbo (Profec B)
'84 RS2URQ
'83 Urq