Re: How do you calibrate EGT and CHT ?

"Jim Williamson" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> "ken" <[EMAIL PROTECTED]> wrote:
>
> >the others in the group may comment on this but I would also caution the
> >location of the thermocouple, if placed in the wrong location - distance
> >from the chamber you will get an incorrect reading. The instrument may
well
> >be correct but if too close or too far away then the resulting indication
is
> >wrong. I would say it is more likely that placement of the thermocouple
is a
> >problem rather than the instrument itself.
>
> And with this in mind I offer that calibration for the EGT is somewhat
> futile.  The EGT reading should simply be correlated to the plug's color.
> The plug is the primary indicator of air/fuel mixture.  It would be nice
to
> go by EGT readings/numbers across the board (plane to plane, installation
> to installation, etc) but too many variables exist - primarily probe
> placement.  The pilot of X craft simply needs to know that at X temp the
> plug (if the engine were to be shut down right then and the plug color
> checked) color would be X color.
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I believe what the individual asking the original question is after is a way
to check his in-flight exhaust gas readings. If this is so it is a valuable
tool for saving parts before they become welded together while you are
trying to enjoy the view from the air. If it is, as suggested, just a way to
check the heat range of the plugs he is using then looking at the plug
itself is good enough.
    When checking plug color you will need to get the engine to normal
operating temp, 3/4 to full throttle, let it run a bit at that setting, and
then cut the ignition. The reason being that if you throttle down before
turning off the ignition and then check the plug you do run a good chance of
getting darker (cooler running) deposits on the plug. This could prompt you
to put in a hotter plug when it is not really necessary.