Re: Some Boost Controller Info

[Robert Houk - WorkGroup Server Firmware <Robert.Houk@East.Sun.COM>]

   The Greddy, HKS, SARD, Apexi, Blitz, etc. are all pretty much the same.  They
   provide a more active control over the wastegate, but because of their
   electronic nature I don't know if it will work with an Ur Q.  Did the Ur-Q
   have an electronic timing valve?  This valve, found on most later models of
   turbo kraut cars, is a simple device the modulates between either positive
   (boost) or negative (vacuum) pressure on top of the wastegate to more actively
   control it.  This is esentially how an electronic controller wires- right into
   the electronic timing valve.  I have seen pictures of the wastegate on the Ur,
   and it seems that maybe it is just spring activated?

The Ur UrQ (the original UrQ, circa early/mid-80's, with MAC-01 or
MAC-02 ECUs) is a purely mechanical wastegate, no ECU control over the
boost.

   Whatever the case, you might want to avoid the "fuzzy logic" controllers like
   the Greddy and HKS stuff, which I know have problems and take time to fully
   program.  Again, some very knowledgable people have told me the only
   difference in units is the color- pick one.  

   Another problem with these electronic controllers is boost hunting.  Most
   stock wastegate's are actually designed to leak, and the only solution is
   getting a new wastegate- one which is more agressive and performance
   orientied.  They can be relatively inexpensive- turbonetics has some decent
   prices.  The point is that the stock wastegate is inaccurate- leaking way too
   much, and the controller has problems with this, sometimes literally searching
   for a stable boost pressure.  

The "drawback" to purely mechanical wastegates is that they are just a
spring. As such, they are "linear" and not just "open or closed". For
example, if you have a "10PSI" spring, when you are running (as a fairly
random pick out of a hat) 7PSI of boost, the wastegate is half open and
bypassing a lot of potential PSI's (you could easily build 10PSI of
boost if the wastegate were still closed). The "fuzzy logic" and other
smart controllers try to deal with this by blocking all wastegate-opening
pressure until (e.g., again a wild random number), say, 9.9PSI have built
up, then allowing enough wastegate-opening pressure to the wastegate to
maintain boost between 9.9PSI and 10PSI. [I do not know the actual and
real numbers, these numbers are chosen purely for explanatory purposes
and should not be used in any real-world scenario/discussion.] This in
principle (executed correctly) accomplishs two things: first it allows
full boost to happen at a much lower RPM than a purely mechanical spring
wastegate can accomplish; and second it maintains the correct boost levels
safely. The purpose of the "learning" process (those full-throttle runs
when you first hook up the beasties) is for the controller to learn the
lag times and other pressure/operational parameters of your engine and
wastegate, so that it can initiate wastegate-opening pressures in time
for worst-case ("1st gear full throttle") boost management and not
overboosting (blowing your engine to bits).

Another nice thing about the smart controllers is that they *can* (as
opposed to "do") compensate for altitude, while the purely spring-
actuated wastegate can only provide a delta from ambient pressure. In
other words, a "1Bar" boost at sealevel (STP) is 2.0 Bar absolute
manifold pressure (a nice hefty boost!); a "1Bar" boost at 10,000 feet
where the "ambient" pressure is only 0.8Bar (anyone know the actual
altitude to pressure correspondence?) is only 1.8Bar absolute. The
smart controller can actually target the 2Bar absolute, and allow a
1.2Bar boost at 10,000 feet in order to accomplish the 2.0Bar goal.
(Of course a drawback of this is that the "smart" controller can
outsmart itself and overrev the turbo in the process...)

					-RDH