EGT Accuracy

[O. Sami Saydjari]

What is the accuracy of the average EGT gauge? Is it plus-or-minus 50
degrees or so? Is it possible to have them calibrated? If so, is it
worth it to have it done periodically? It seems that alot is at stake
if the gauges are not acurate.

My PA-28R-201T POH says that temperatures of 1650 degrees are
"allowable." My EGT's never get above 1420 even at the absolute peak.
Does that mean I am "golden" as far as temperatures go?

-Sami
N2057M, Piper Turbo Arrow III

[James M. Knox]

"O. Sami Saydjari" > wrote in news:105d6vadm8klu68
@corp.supernews.com:

> What is the accuracy of the average EGT gauge?

GAMI did some checking on this early on... using NSTI calibrated
equipment for comparison. A modern GEM or JPI gauge should be accurate
to within about a degree or so... fantastically accurate for such
equipment (assuming it's not just plain broken).

However (!!) placement of the EGT probe is so sensitive that the actual
readings you get are pretty much arbitrary. As long as all of them are
placed identically, you will get very accurate readings AT THAT POINT,
but it's really more of a "comparison" thing than an exact specific
number.

> My PA-28R-201T POH says that temperatures of 1650 degrees are
> "allowable." My EGT's never get above 1420 even at the absolute peak.
> Does that mean I am "golden" as far as temperatures go?

Well, first off, 1650 is NOT a temperature you want to operate at! It
just means that if you don't go above that then most of the metal in
your exhaust and turbo will only have gotten soft, not actually melted.
{:<)

EGT's of 1400 - 1520 are a nice range. [Your TIT can read almost 100 F
above the EGT, although I seldom see that.] I'm a bit surprised you
never see anything higher... sounds like you are running very rich.
What do you usually use for cruise? And what are the corresponding temps
and fuel flow?

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

[O. Sami Saydjari]

>
> EGT's of 1400 - 1520 are a nice range. [Your TIT can read almost 100 F
> above the EGT, although I seldom see that.] I'm a bit surprised you
> never see anything higher... sounds like you are running very rich.
> What do you usually use for cruise? And what are the corresponding temps
> and fuel flow?
>

Actually, I am able to run about 40 degrees lean of peak and the
temperatures at cruise are about 1380. Fuel flow is about 11-12 gals
per hour.

[James M. Knox]

"O. Sami Saydjari" > wrote in
:

> Actually, I am able to run about 40 degrees lean of peak and the
> temperatures at cruise are about 1380. Fuel flow is about 11-12 gals
> per hour.

Okay, here's something "interesting." You are running pretty high power
settings there... up probably around 85% (at 12 gph LOP). At LOP it's
probably okay to cruise that high (because the pressure pulses are lower at
peak, and more spread out). How's your CHT's?

I typically cruise at 10.5 gph (75% power LOP), with the RPM back down to
around 2300. My EGT's will be in the 1450+ range. CHT's will be down
around 300 - 340 or so. Interestingly enough, the time I see really high
EGT's (trying to push over 1550) is low power, down at about 25" or less.
An annoying side-affect of our fixed-timing engine ignition systems.

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

[O. Sami Saydjari]

James M. Knox wrote:
> "O. Sami Saydjari" > wrote in
> :
>
>
>>Actually, I am able to run about 40 degrees lean of peak and the
>>temperatures at cruise are about 1380. Fuel flow is about 11-12 gals
>>per hour.
>
>
> Okay, here's something "interesting." You are running pretty high power
> settings there... up probably around 85% (at 12 gph LOP).

Well, I should say that my fuel flow gauge says 12 gph, but my actuals
are closer to yours at 10.9 gph.

> At LOP it's
> probably okay to cruise that high (because the pressure pulses are lower at
> peak, and more spread out). How's your CHT's?

Growl. I do not have valid CHTs at the moment because of a poor job
installing a tanis heater. I will have this corrected next month. I
hate being blind to my CHT readings. And I just baught my plane, so I
do not know what the CHTs notmally run.

>
> I typically cruise at 10.5 gph (75% power LOP), with the RPM back down to
> around 2300. My EGT's will be in the 1450+ range. CHT's will be down
> around 300 - 340 or so. Interestingly enough, the time I see really high
> EGT's (trying to push over 1550) is low power, down at about 25" or less.
> An annoying side-affect of our fixed-timing engine ignition systems.
>
> -----------------------------------------------
> James M. Knox
> TriSoft ph 512-385-0316
> 1109-A Shady Lane fax 512-366-4331
> Austin, Tx 78721
> -----------------------------------------------

[James M. Knox]

"O. Sami Saydjari" > wrote in
:

>> Okay, here's something "interesting." You are running pretty high
>> power settings there... up probably around 85% (at 12 gph LOP).
>
> Well, I should say that my fuel flow gauge says 12 gph, but my actuals
> are closer to yours at 10.9 gph.

Those old analog gauges for FF are pretty inaccurate. They aren't
really fuel flow gauges anyway. They are pressure gauges, calibrated to
read out in gph, on the theory that a certain pressure through a certain
combination of injector sizings will equal a certain fuel flow.

When ROP the power setting is pretty much independent of fuel flow,
since excess fuel is discarded out the exhaust. When LOP all of the
fuel is consumed and the power setting is directly a function of the
fuel flow. Of course, then what the power setting actually means is up
for grabs (ever wonder how you can have in your POH two different
performance values for the same "75% power"?).

> I hate being blind to my CHT readings. And I just baught my plane,
> so I do not know what the CHTs notmally run.

Limit on that plane is 460 F, but that's WAY TOO HOT for normal
operation. The manual recommends 400 or below, and that's good
practice. I like to keep mine under 380. Usually, except when hot and
heavy, I keep them down more like 330 - 350. The big problem isn't the
high temperature so much, but rather the fact that the temperature
around the cylinder is very non-uniform. So while your probe reads 330,
a spot on the other side could be 260, or 420.

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

[Roy Smith]

In article >,
"James M. Knox" > wrote:

> (ever wonder how you can have in your POH two different
> performance values for the same "75% power"?).

Depends whether you're on the step or not :-)