RE: Turbo questions - K24, WG Spring etc.

["MLP" <mlped@concentric.net>]

Javad, we may be talking at cross purposes, but a spinning blade, by itself
does not create boost.  i.e. you can wrap you engine to 7,000 rpm and still
be running on manifold vacuum, even on a turbocharged engine.  Granted, once
you dump a load on an engine turning 7,000 you should see an immediate jump
in boost, then overboost, as opposed to a slow buildup

Further, I don't believe that the wastegate ever bypasses all the exhaust
gasses, it just bypasses excess gasses.  The point I'm trying to make is
involves the concept of "boost" occurring "sooner" in a given rpm / load
range - simply as a result of shimming or using a heavier spring.  The
strength of the spring has no effect on the initial build up or presence of
boost; it may prevent overboost from "leaking" away sooner, i.e. the "creep"
you don't want, but it I don't think it will cause an otherwise "unboosted"
engine to come into boost faster.  Further, I think that if the other
components of the boost control system are working correctly, the ECU should
be providing the pressure needed to keep waste gate "creep" from occurring.
But maybe that's in an ideal world....  I think the S-car engines are
supposed to be set up to operate this way.  I don't know about the earlier
Audi turbo systems.

Mike P.


-----Original Message-----
From: JShadzi@aol.com [mailto:JShadzi@aol.com]
Sent: Tuesday, November 23, 1999 8:13 AM
To: mpederson@bigfoot.com; BSWANN@arinc.com; quattro@audifans.com
Subject: Re: Turbo questions - K24, WG Spring etc.


In a message dated 11/23/99 3:06:12 AM Eastern Standard Time,
mlped@concentric.net writes:

<< Why stop with shimming the waste gate closed if that made more boost
 "sooner", i.e. at lower rpm?  Why not weld it shut.  Welding or shimming
the
 waste gate doesn't "make" boost - all the waste gate does is allow you to
 control the boost once it's already there.  It does not make boost occur at
 lower rpms.  If you think about it, all a stiffer spring, or shimming does
 is prevent boost that's already there, in the system from being bled off at
 the waste gate.  And, if the shim or spring is set high enough, it will
also
 prevent the ECU from doing its job of regulating boost as well.
  >>

    I think what is being reffered to here is known a "boost creep", or the
condition when the waste gate spring is not initially stiff enough and
allows
the wastegate to crack open at a pressure level well below its maximum.
Also, the wastegate controlls exhaust flow to the turbo, not boost, which in
turn produces boost.  The two variables you mention, RPM and load, do
nothing
more than create additional exhaust flow to spin the turbine.  The wastgate
is controlling boost essentially by controlling what created boost: exhaust
flow.  A stiffer spring will also allow more overall boost by forcing more
exhaust gas past the turbine, spinning it faster, and creating boost.
Higher
RPM and throttle opening will not create more boost if all the exhaust
manifold pressure is being bled off by the wastegate, right?...
Javad