EGT balance issues

[mike.smith]

Mike,
I agree CHT is the #1 concern. But don't you worry about going over the 1400F EGT redline? I assume it's there for the health of the exhaust valve and seat.

EGT is incredibly dependent on where you put the probe, how accurate the probe is, and even the type of wire used. I was being extreme with the 2,000 deg data point, but the gist is that if the CHTs are all in the green, then it's unlikely the exhaust gases are at a temperature where they are doing any harm.

And trying to match EGTs is a total waste of time, if everything else is working fine. I've been seeing 100-200 deg differences for over 10 years. When I see trends, like one EGT that is above or below the norms for that cylinder, that's a useful data point. That's what EGT numbers are best for.

Mike Busch on some of this:
https://www.savvyaviation.com/wp-conten ... bunked.pdf

And again, knowing some of the numbers for this engine would be helpful in the review.

[Scott Todd]

Thats a great article! While Sonex tries to star fairly neutral, I'll toss in my two sense after owning 3 AeroVee's and flying 3 others. All of them were set-up and 'tuned' by me per the Aerovee manual. They NEVER match :) I've tried rotating the carb (injector) housing with limited success. The ones I set-up and the ones I've helped others with high CHT's were easily traced to cooling airflow issues. My current ride is a Onex with a new Aerovee. It only has about 50 hours on it but here is how it goes.

The EGTs run within about 50-60 with he exception of number 2 that runs about 100 low. So in cruise at 3250 the EGT's run around 1150 with one around 1050. The CHT's run around 320 with number 2 running around 280. Of course these are bouncing around but what I noticed last night after flying laps around the airport for 30 minutes. I'll dump the data when I get a chance and try to get some more accurate trends. I run full rich. Its too rich at idle but I like how it runs upstairs. Full power static is around 3050 and in the air it will go to 3400. I can lean it in flight and see the temperatures rise and the fuel flow go down. However, I don't mind paying for the fuel and I like the low temps. It usually shows around 140 mph at 4.0 gph. You can go look at my ADSB data from last night if you like :)

I had a nice conversation with Jeremy several years ago about the size of the Onex inlets. He said something about not wanting cooling issues and was willing to pay for it with a few mph's of speed. He was dead on. The Onex's I've been around never have cooling issues :) I always tell people not to worry about the EGT's and make sure the CHT's are reasonable to be nice to the the engine. I won't consult on cooling for race planes and tell all the other folks that ask for cooling help to seal the baffles, open that exit, increase the lip, and who cares if it slows you down an tiny bit ;)

Scott
N23092
We have a saying around my airport. "Fly it and watch it"!

[peter anson]

Because all the advice said to not worry about variation in the EGTs too much, I didn't. All the CHTs were low so all good. Now it may be just coincidence, but when one of the exhaust valves failed it happened to be on the cylinder that always had the highest EGT. I can't recall seeing it get higher than around 745C (1373F). On my new engine I decided to try to limit EGTs to 700C (1292F) and I now have a fairly even spread of temperatures, achieved mainly by using a crossed vane flow straightener ahead of the carburettor. Rotating the vanes by quite small amounts has a noticeable effect on EGTs.

Peter

[petep]

Update - Tried the modified spacers and intake elbow with only a minute change, Reinstalled orginal spacers and stock Great Plains intake elbows. Ran a WOT test with the air filter removed and the EGT zoomed high on all four cylinders. Looks like I need to get more fuel into the mixture so I tried a 2 1/2 needle with some improvment but still can not sustain WOT without blowing thru 1500 EGT. Installed number 3 needle and saw a decent improvment right off the bat. Life has kept me pinned down and have not been able to do more WOT runs. It seems at this point that nether the number 2 or two and half needles have a steep enough taper to get to enough fuel flow to get the EGTs down to even near 1400 without being so far rich that I can hardly shut down with mixture. The number 3 needle has promise but can not be sure utill I can do more tweaking and WOT runs. Sonex says to enrich the needle position so you can achieve a 90 to 100 degree when leaned at WOT. I will be happy to get to the pont where I can sustain WOT with out exceed ing 1400 degrees. So far the CHTs have all been acceptable but I have not been able to sustain anywhere near WOT long enough to verify the CHT in a prolonged flight.