Re: Controlling Turbo boost

[rdh@sli.com (Robert D. Houk)]

   >.. in 1st and 2nd gears,
   >the RPM/Boost build too fast and can cause the ECU to overboost-cutout
   >before the air pressure regulator as settled and stabilized at it's
   >lower-than-peak holding point.

   I don't quite follow here Robert.  My experience, although limited,
   is that boost fed counter-pressure rises slowely.  Less counter-pressure
   means less boost, thus how do you get over-boost.  Is the counter-
   pressure left over from first gear as you shift into second?

No - it "takes a second" for the air pressure regulator to stabilize at
4.0 (nominal) PSI, after peaking "briefly" at nearly 5 PSI while the
turbo builds up boost. In (e.g., 3/4/5 gears), as I run the engine up,
I can see the boost go up to 15, then "settle" back to 14 as the regu-
lator stabilizes; in (e.g.,) 1st gear, if I run the engine up ("punch
it"), I'm at redline/high rpm and the boost is too high because the
regulator hasn't yet backed off from its transient overpressure. Note
also that my turbo "stock" builds 10PSI at 3000 and 12PSI at 5000, which
is I think the bigger bug (12 + 5 = 17 == overboost and the ECU cuts
out, but 12 + 4 = 16 and I'm safe, in 3/4/5 gears where the regulator
has stabilized at 4PSI adjustment -- at 3000, it's 10 + 5 = 15 PSI,
which is not overboost, and by the time it gets to the higher rpms where
it is "naturally" putting out higher boost, the regulator has stabilized
at the lower 4 PSI offset).

So half the question (well, it's a full question in its own right) is
why does the turbo build up 12PSI at 5000, and not stay at 10PSI, as
at 3000rpm. Is my wastegate sticking? Could the S4 turbine/housing
actually be too small (and sensitive, so even with the stock wastegate
wide open, it still spins "too" fast? (i.e., do I need a bigger waste-
gate, or bigger ex- haust turbine? Now if someone ever gets their RS2
act together and starts offering them to all'uh'us nut cases...)

The other question is how to get the air pressure regulator to stabi-
lize "faster" (I could use a "tank" and store pressure...). My conclusion
is that I will probably have to go to a electronic control to get any
more precise control over the boost level (or disable the ECU's over-
boost code, which I don't wanna do, or just live with not being able
to get that last PSI.

					-RDH