WGFV Funtion

[QSHIPQ at aol.com]

Phil Payne writes (>>)
> 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.

>>Oh, I don't know.  I found the difference between 1.35 bar and 1.85 bar
>>on my MC-2 with Scott Mockry's spring and chip pretty 'noticeable'.
>>Audi's stock claim is 165 bhp - I reckon I'm now between 220 and 230
>>bhp.

Phil, you need to understand that the difference between the springs is 
noticeable because you have addressed the shortcomings of the WGFV, nothing 
else.  For an excersise in understanding, put a 2.0bar spring in your car and 
unplug the WGFV all together, you might see something that will surprise you. 
 1.85 bar is *NOT* 220 or 230hp, maybe 200.  To get more than that, you'd 
need 2.0 (1.95 exactly) mod, which on a REALLY cold day, you might be able to 
claim 220 with no other mods.

> Basic misunderstanding of boost, and how it works.
>>Tsk - there we go - my basic misunderstanding of all things technical
>>again.

I'm only looking at what you wrote vs what really happens Phil.  If you put 
manifold pressure on top of a wastegate directly, the turbo blows up, and 
fast, specifically *fastest*.  You seem to think that adding a spring to that 
will make it blow up faster.  NO, not *unless* you are using a percentage of 
manifold pressure to the top of the wastegate.  That said, remember that the 
fault of the audi WGFV (top feeders) is their  design inability to clamp the 
wastegate shut with low boost levels, causing Wastegate cracking problems.  
Stepper motors can sut the wastegate completely at any boost level.

> 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.

>>Actually the MAC11/12D/14 WGFV is connected to both 'vacuum' and 'boost'
>>inputs and uses both to modify the effort exerted by the spring.  Its
>>major functions (at least according to Audi) are to reduce turbo lag and
>>facilitate achieving the design power output with some precision - this
>>is an issue with the TueV in Germany and purely mechanical solutions
>>such as those used in the WR were no longer acceptable.

The precision maybe acceptable on a stock car, it isn't on a tweeked one.  
Claiming the vaccum helps pull the WG open is rather misleading, it can, but 
if you really look at what's happening under vaccuum and it's source, what 
difference does it or can it make.  You are somewhat correct that the WGFV is 
used to address turbo lag, but it really doesn't because of cracking.  Where 
it does help somewhat is in the slight peak of the .2bar it adds on top of 
baseline spring pressure.  This allows for additional boost levels if 
conditions are right, and assures that all cars leaving the factory have 
roughly the same boost level, all engine production tolerances, delivered to 
any customer worldwide.  This is old technology, stepper motors take that 
wave out of the  FV function loop, and make it linear.

Where this all falls flat on it's face is when one tries to use a POS WGFV to 
modify high boost level modded cars.  Neither device is capapble of handling 
that well, and the devices exacerbate the faults of WGFV inherent designs.

> It's major function is to provide a safety net ...

>>It has nothing like the scope of operation.  Disconnect the middle chamber
>>hose on a 10V and see how much control it has - you'll go straight to
>>fuel pump cutoff.

Wrong test Phil.  Disconnect the WGFV, add a stiffer spring or shims, your 
boost can ramp faster than the WGFV.  The problem is that if a bad input 
comes in, you have nothing to help you lower the boost.  Disconnect the WGFV 
in a gen II turbo car (bottom feeder) you will get 1.3 bar all the time.

>>It's true you don't necessarily need a wastegate spring change on the
>>newer cars.  The S2 Avant I'm currently working on was lifted to ca.
>>285 bhp by software alone.  I've never noticed that the WGFV on these
>>cars is particularly prone to failure - I've had three failures on
>>MAC12D cars, but I've never seen one on a Motronic car.

I can send you a dozen if you like.  Or try subbing to the 20020v or the S 
car list.  This is not only a known failure component, it's a major bitch 
amoungst the guys that have bought their 3rd in a couple years.  They are 
known to leak quite regularly, the more boost applied to them, the quicker 
they fail.  And like hard drive failure, it's *not* an if...  Not easy to 
diagnose either.

HTH

SJ