[s-cars] WGFV-Sunday night ponder.

[Djdawson2 at aol.com]

Bill,
In the simplest terms, the WGFV does one thing: it regulates the amount of 
boost pressure given to the engine.  It does this by either "adding" to, or 
"subtracting" from the wastegate spring pressure.

As boost climbs, the pressure inside the exhaust manifold builds.  At a 
certain point (about 2 bar absolute when using a stock WG spring) the pressure 
within the EM exceeds the spring pressure on the wastegate valve.  When that 
occurs, the wastegate valve opens, and exhaust gases are permitted to pass around 
the hot side of the turbo... boost is then reduced.

If you look at your WGFV, you'll see that it is supplied with both vacuum and 
pressure.  Vacuum comes from the hose connected to the turbo intake boot, and 
pressure from the turbo compressor housing.  The third line at the valve goes 
up to the wastegate.  The wastegate has a diaphragm in it, and the line is 
connected on the bottom side of this diaphragm.  If the WGFV allows boost to go 
to this chamber, it is, in essence, weakening the holding power of the 
wastegate spring... boost drops.  If you apply vacuum to this chamber... the spring 
is "strengthened"... and boost increases.

If you disconnect the WGFV, you'll see that its failure mode is to allow 
boost pressure to the chamber, thus keeping your max boost to a very low level... 
a safety feature.  On the other hand, if you were to take a small pair of 
needlenose vicegrips and clamp off the line to the wastegate, you will see that 
your boost level should max at about 15psi (1 bar, 2 absolute), as now boost is 
only controlled by the wastegate spring, as you've taken the WGFV completely 
out of the equation.
HTH,
Dave in CO