[s-cars] Overboost and Wastegate Springs

[David Forgie]

One of the things that waste gate springs provide is the minimum boost levels.  You can see this if
 you disconnect the N75 WGFV.  On a stock spring and perch height this is about 6 psi.

As far as I know, when people talk about the number of "Bar" a particular wastegate spring is 
rated at, e.g. 1.4 Bar or 1.9 Bar, they *should* be talking about absolute pressure, not relative
 pressure.  A stock 1.4 Bar spring is about 20.3 psi absolute or about 6 psi relative.  Likewise,
at 1.9 Bar spring is 27.55 psi absolute or about 12.8 psi relative. These are the maximum "minimum"
boost levels.

My experience with a 1.9 Bar spring was at the stock spring perch height, it resulted in too rapid
initial boost rise, which freaked out the ECU, causing it to dial back the boost via the WGFV, then
it would try again, and the rise rate would be too high, again a dial back, all in fractions of a second.
This resulted in a very jerky stacatto effect.  Not nice.  Solution: Turn the spring perch up until the 
issue is removed. Still provides a good initial tip in boost level. (IME). 

Some N75 info: http://forums.quattroworld.com/s4s6/msgs/20987.phtml

But you knew that. ;>)

Dave F.