Re: Turbo questions - K24, WG Spring etc.

[JShadzi@aol.com]

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