Re: Exhaust temps

[QSHIPQ <QSHIPQ@aol.com>]

In a message dated 97-11-06 12:40:09 EST, you write:

<< Several have asked about egt's and one has said the same are irrelevant.
>Turbo or not, egt's are not irrelevant.  This is not rocket science, not even
science at all, just common sense.  If egt's >were irrelevant, ask yourself,
why are guages manufactured to measure the temps?  Why do engine builders use
the >guages?  Any pilots out there?
> Bruce   
   >>

Let's not misquote me counselor.  My EXACT quote is:

BRUCE -  "I have asked several questions about egt's and have been told the
same is irrelevant to you."  
 
QSHIPQ   - "FOR THIS discussion, they are.  So are your assumptions of EGT on
turbo motors"

You are making assumptions regarding EGT and turbos.  EGT, even in aircraft,
are not turbo application devices (save a push/draw thru turbo carb system I
suppose).  They are for adjusting Rich/Lean Fuel vs altitude (higher altitude,
you lean the mixture = Less pounds of air at higher altitude>less pounds of
fuel needed (higher EGT indicates lean/lower indicates rich)  What is
different with turbo car example?  Higher PR/lower DR = Less pounds of air>
less pounds fuel needed).  Why do you care what baseline EGT is if you have
"lamda" fuel doing all that Rich/Lean adjusting for you?  And lamda IS
altitude compensating, built right in (audis up to 14,000ft anyhow) to the
machine.  Why do folks have them on street cars?  Well, another tool for
making sure all is well upstream while the car is running, assuming a
baseline.  You are trying to make it an indicator that the turbo is correct.
How, I ask?  What does it tell you, Bruce?  This cow is still out to lunch on
your point.

 I forwarded your post to Lister Pilot Rob Dupree for his input, since my
credibility might be with conflict of interest.  Rich/Lean Fuel has little to
do with choosing a turbocharger via a MAP, specifically NOTHING.  Should it?
In accepted theory and practice, it doesn't.  A reason for that perhaps should
be considered.  In fact, it's irrelevent to every formula presented so far,
hence my urging to you.  All formulas and MAPS ASSUME you can get the fuel for
given pounds of air.  Can't?  Get a bigger injector.  Still can't?  Get a
bigger injector.  

Anyone can show you that one compressor may generate more heat than another.
EGT is a great tool for indicating to the driver that something is wrong
upstream.  For a N/A car, Rich/Lean maybe.  For a turbo car, more.  Could
indicate Rich/Lean, could indicate a turbo heat soak.  Could indicate a
different turbocharger.   So, if you saw 1350 EGT on a guage in a car, and
don't know what turbo it is, what would a different turbo with a higher EGT on
the same car tell YOU?  Why?  Since there is only one probe of that 1350,
where did you locate it?  Is it average of 5 cylinders, or average of 5
cylinders and a heat generating pump?

I claim, EGT is irrelevent here.  Not until you know what is upstream.  Dave
or I can, by math, knowing what is upstream, tell you what EGT should be.
Going EGT first, sure is going up the downstream elevator.  This is nothing
more than thinking exercise.  It doesn't except the math presented, only makes
it more complicated.  Why do that?  You yourself admitted that what's been
presented is beyond your math abilities.  Is EGT relevent as a concept?  I
suppose.  Is it relevent to "choosing" a turbocharger?  No.  Is it relevent to
the "mods"?  Only that it "seems" enough fuel is getting to the cumbustion
chamber given 2.79PR.   Ok, as stated in my original post.  

Scott