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EGT Probe location

cdeerinck

Well Known Member
I am getting ready to drill holes for the Dynon EGT probes in my Vetterman dual muffler exhaust.

In reading, I have learned the following:
1) Clock them any way that works for you, but keep them the same distance
2) Don't put them on a bend
3) The closer to the engine, the more responsive the readings will be
4) Too close to the engine, and you will burn them up
5) Too far from the engine, and they will be slow to register changes
6) Ideal distances for a Lycoming are in the 2 1/2" to 4" range

Can anyone tell me why rule #2 is true? Is it because the hose clamp won't conform, or because it will bite harder on the edges on a corner and risk a crack, or because the gas does different things around a bend, or something else?

The reason I ask is I can get a 2" distance at best given my pipes. I would prefer 2 1/2" or 3". But one of the pipes starts a 45-degree bend at about the 2 1/4" mark.

If I put the probe at 2 1/2", it would just be at the start of the bend. Would that work, or am I asking for trouble?
 
EGT Probes

Here is exert from my build log. I have the same exhaust.

I installed the exhaust gas temperature probes. Directions say to go by Lycoming's recommendation but I couldn't find one. There was a note in Van's plan that says mount them 2 - 5 inches from flange but wasn't very specific. So I called Vetterman's since this is his exhaust system.

He was a great guy to talk to. He told me explicitly to mount them 2 inches from the flange. because there is already 1/4 inch taken up by the flange and 2.5 inches is ideal so 2.25 from the flange would be okay to. He also told me it is VERY important to make them all the same distance to within 1/16th of an inch. He said 1/16th inch difference will yield a 100 F degree difference in reading. He also told me to use a cut tie wrap to measure. And most importantly he told me which way to point them for each exhaust. Basically you avoid interference with the spark plug access.

#1 points forward. Points mean the hot end forward and the wire trailing end rearward.
#3 is 45 degrees facing rearward to avoid interference with spark plug
#2 is 45 degrees facing forward to avoid interference with spark plug
#4 pints straight back

Photos here: http://www.mykitlog.com/users/displ...n&project=607&category=6898&log=245644&row=19
 
I have the same exhaust.

Steve - Thanks, that helps a lot. Great pics, but evidently my pipes are very different (perhaps because they are for an RV-8). I have a captured slip joint about 6 inches on pipes 1 and 2, and they do a crazy s-bend before joining pipes 3 and 4.

Despite those differences, you gave me exactly the information that I needed regarding the spacing. I will put mine at 2 1/8" from the flange, and will clock them to avoid interference.

One question remains. Since you said the distances are so critical. My pipes 1 and 3 have a slight bend in them (maybe 15?), similar to yours and I am wondering how to measure "around the curve". Any suggestions?
 
Measuring the bends

Chuck
For measuring the bends use a length of tie wrap, because the tie wrap is flexible. The idea is to measure down all around the pipe with the tie wrap length, mark it, and that should be 2 1/8 from the flange.

Now that I'm flying my egts are within 100F of each other, but the egts are not really very meaningful, except for leaning. So close is good enough.

Have Fun...
 
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