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What is the recommendation for EGT probe locations on the Aerovee?

On my R2300 (RevMaster) I have the probes drilled about 4" from the flange. They are very slow to respond thus not very useful for leaning.

I think mine are closer but also respond slowly. I would assume the distance affects the magnitude but not the quickness. There is a lot of flow so an inch or two won't change the timing. Probably a probe issue, or filtering in the MFD.

The Aerovee manual says they "must be installed 4" from the exhaust flange of each cylinder [...] based on a path down the center of the exhaust pipe." Sounds the same as your installation.

It does take a little while to respond, but I've never given much thought to it so can't comment to whether it's the same as what you see or not. It doesn't seem excessively long though. I mostly lean by feeling the RPM increase/roughness and use the EGTs to confirm my feelings.

gammaxy wrote:The Aerovee manual says they "must be installed 4" from the exhaust flange of each cylinder [...] based on a path down the center of the exhaust pipe." Sounds the same as your installation.

I'll have to check the next time I have my cowl off. They are wherever Mike Farley put them.

Thanks All for the input. I'm normally careful about installation of things like this where holes have to be drilled. So I likely got them in the correct place. Must be the MGL filtering/averaging.

I don't think the slow response is anything to do with the MGL. Rather it is due to the "thermal mass" of the probe itself. The thermocouple (at least the ones on my engine) is encased in a stainless steel tube which has to heat up first. I encountered this problem with temperature control of a laboratory furnace years ago. The control thermocouple was made of very heavy wire which responded much more slowly than the fine thermocouple wire that I was using to check the system. The best you can do is try to source sensors that are as small as possible.

Peter

peter anson wrote:I don't think the slow response is anything to do with the MGL. Rather it is due to the "thermal mass" of the probe itself. The thermocouple (at least the ones on my engine) is encased in a stainless steel tube which has to heat up first. I encountered this problem with temperature control of a laboratory furnace years ago. The control thermocouple was made of very heavy wire which responded much more slowly than the fine thermocouple wire that I was using to check the system. The best you can do is try to source sensors that are as small as possible.

Peter

thank you, peter.

Hopefully you can learn from my mistake.

I dutifully measured 4", and installed the probes. Later, when I fit the cowl, I found that the locations on #2 and #4 interfered (hugely) with the inside of the cowl. I had to bend them nearly 90 deg, and even then they still rub. And when I bent the first one, I broke it and had to order a new one. Don't bend them! So I would suggest you don't install the probes until you fit the cowl.

As for the 4", don't sweat it. Just make sure all 4 use the same distance. EGTs are good for troubleshooting, showing trends, and leaning. But using them as absolute numbers is pointless. Try reading: https://resources.savvyaviation.com/wp- ... bunked.pdf

It's CHTs that really count, not the EGTs.Think of it this way. If you install the EGT sensors 3" from the exhaust ports (I'm not suggesting you do), maybe you see temps of 1700 F. "Ooohh, nooo, that's too hot!" But if your CHTs are below 400 F, then that's what matters.

mike.smith wrote:Hopefully you can learn from my mistake.

As for the 4", don't sweat it. Just make sure all 4 use the same distance. EGTs are good for troubleshooting, showing trends, and leaning. But using them as absolute numbers is pointless. Try reading: https://resources.savvyaviation.com/wp- ... bunked.pdf

Unless you fly behind a Jabiru engine whereupon the factory has specified absolute EGTs that should not be exceeded for different power settings. If I recall accurately, it has something to do with broken valve stems. I wouldn't want someone to be misled by recommendations that may more appropriately be applied to Lycoming and Continental engines.

Art,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,Jabiru 3300 #261

builderflyer wrote:... I wouldn't want someone to be misled by recommendations that may more appropriately be applied to Lycoming and Continental engines....

Yes, that's good advice. In my case, I'm driving a RevMaster R2300 (comparable with the AeroVee) which has a max EGT limit of 1400˚. So I do watch out for that and my probes seems to be adequate for that kind of monitoring.

Though, I'm most familiar with Lycomings and yes I'll run them hotter (especially when LOP). So part of my questions stem from the fact that I'm still learning about the VW variety of engines.

I take everything on any forum with a grain of salt.