[s-cars] safe boost limits - Wastegate 101

[QSHIPQ at aol.com]

No Rod.  Large WG springs (or adding preload to the stock) add low end
torque, because you are changing the ramping of the WGFV circuit (please
continue reading, I don't consider this a *good* thing).  If you put in a
1.5bar spring for instance, when the WGFV wants to trim boost, it can only
trim it to 1.5bar.  A 1.5 bar spring however will only allow 1.5 bar boost
without WGFV assist.  The only time I've seen boost "added" to the high end,
was putting on a 2.2bar spring on a 2.1bar car.

So the assessment is correct as stated, Adjusting WGFV preload does little,
and the baseline spring pressure (WGFV fully open) is 1.3-1.4bar (5-6psi).
You may or may not see that depending on the mods you have in your car.   For
instance, a huge turbo with WGFV bypassed will pop the WG WFO (a combination
of turbo map and wastegate cracking).  By definition, if there is a spring in
a wastegate, with *no* electronic control, you must have some boost.

I recommend *against* messing with WG springs.  They are there to protect
your engine investment.  A better way to address the crappy WGFV is to adapt
a stepper motor into the software. Stepper motors are much more accurate than
the FV approach audi chose.  The problem with them is that the software has
to be changed to accomodate them.

Also note:  Bypassing the WGFV isn't a good idea either.  Remember, without a
software change or a input fault, the computer will be looking for that
16/22/26psi, and will ramp your turbo up to overcome the WG blowoff.  If all
goes well in this scenario, your MAF will code you out before you blow the
turbo.  That is not always the case, btst.

HTH

Scott Justusson
QSHIPQ Performance Tuning




In a message dated 9/18/02 2:09:25 PM Central Daylight Time,
S4audinut at aol.com writes:


> From what I have read on the list the wastegate spring limits max boost to
> only 1.3 bar Abs, and the WGFV is what is allowing the overboost to get
> where it is.
> Is this a correct assumption, if so... winding down the wastegate would do
> little, would it not.
>
>

No, The WG spring has more to do with getting these unacceptably high levels
(unless engine totally built) than any SW. I have some VERY aggressive SW and
it doesnt run this high when not in overboost.
Rod