Strange EGT behavior, maybe

[hazek]

Could some Bravo driver please share their engine data for a flight or two recently flown. Especially if when you set descent power you reduce MAP and then set 2000RPM and lean to peak(or rather your TIT limit). And then go rich only shortly before landing. My EGTs behave strangely and I’m investing it. Example:

https://apps.savvyaviation.com/flights/shared/flight/9918044/7b2f4c42-0682-4108-bc82-6710a969fd1a

See at 00:29:45 timestamp, EGT3 stops being hottest and moves to middle of the pack just as I reduce RPM to 2000 for the descent. Then as I go mixture rich the order switches again and EGT3 is hottest again.

 

My main question is if this is normal behavior, i.e. do other Bravo drivers see the same?

[Rick Junkin]

I don’t run my engine that way so I don’t have data for a useful comparison, but I wouldn’t worry about what you’re seeing.

You’re changing all three variables, RPM, MP and FF/mixture, so I’d expect to see some variability in EGT for each cylinder and between cylinders as the changes are made. Those changes impact both fuel and air induction slightly differently for each cylinder. My EGTs can swap order when I go from ROP to LOP, although they’re all within about 80° of each other. That has more to do with the placement of the probes though.

What is your GAMI spread, and in what order do the cylinders reach peak EGT? That may provide some insight as to what behavior you can expect at your different power settings.

If you’re concerned, take a look at how this flight compares with your other flight data. If things look fairly consistent across flights, I wouldn’t worry about it. 

[Fritz1]

EGTs can vary between cylinders based on probe position and probe angle, the exhaust runners in the Bravo engine are short and not well tuned, flow patterns in the exhaust runners vary with rpm, throttle position and fuel flow, thus temp, keep your TIT below 1580 and your CHTs below 480, the engine will purr and more than likely make TBO, Gamis and fine wire plugs help in the Bravo engine, I run the engine at 2250 rpm 30.5" for max continuous cruise, lower rpm and higher boost appears to produce more complete combustion, thus lower EGTs, when stretching range I reduce power to 2250 rpm 26" while maintaining 1580 TIT

[Fly Boomer]

2 hours ago, Fritz1 said:

EGTs can vary between cylinders based on probe position and probe angle, the exhaust runners in the Bravo engine are short and not well tuned, flow patterns in the exhaust runners vary with rpm, throttle position and fuel flow, thus temp, keep your TIT below 1580 and your CHTs below 480, the engine will purr and more than likely make TBO, Gamis and fine wire plugs help in the Bravo engine, I run the engine at 2250 rpm 30.5" for max continuous cruise, lower rpm and higher boost appears to produce more complete combustion, thus lower EGTs, when stretching range I reduce power to 2250 rpm 26" while maintaining 1580 TIT

I know Lycomings are tougher than Continentals, but 480 sounds high.  

[Fritz1]

Yes, meant to say 380 CHT, 480 absolute meltdown

[hazek]

Thanks for the input so far. But would be cool to see some of your flights’ data and compare. Yesterday my plane was looked at and an induction leak was confirmed on nr5 cylinder. Something that Savvy predicted based on my data. The gasket was completely destroyed and the induction manifold was covered in telltale blue stains. (see pic)

The flight I shared was prior to that being fixed. Since Savvy saw a problem I’m just curious how my data compares to everyone else. Perhaps that leak was not the only problem. Perhaps how my EGTs behave during various phases of flight might show something else. But I’m also getting the “too much data for such a crude machine” line, and that I can’t expect temps to behave exactly to expectations. Well, one the hand I agree and entirely see the point but on the other hand seems like data can indeed show a problem and it’s not just variability.

So again, would be really cool if we could compare a bit. Especially those of you who have a very nicely tuned Bravo, something that’s very hard to get to over here in Europe with so little expertise available. Don’t be shy, you can share also just in a private message, I will not abuse your privacy. Just really am looking for more data and trying to establish a baseline expectation for my plane.

[Fritz1]

well looks like you are getting somewhere, do not have data logging on my EDM 700, looking at the intake, check the spouts that run into the oil sump, blue stain shows leak, there is a Lycoming tool to swedge the bead in the short spouts so they seal against the oil sump again, tighten all clamps on rubber connectors of the intake tubes, baffles should press snug against the cowl, replacing dead pieces and sealing all nooks and crannies with RTV can really drop CHT, any light that shines through the baffles indicates lost ram air, keep pushing and your bird will be fine tuned on no time

[Rick Junkin]

Here's a flight where I was gathering data at different power settings both ROP and LOP, and did a GAMI sweep in the middle of it all. It shows the variability that occurs across the cylinders as you change combinations of RPM, MAP and FF, and how the EGT and CHT relationships are different ROP and LOP. To your mechanic's point about too much data for a crude machine, yes, there is going to be variability from one flight or power change to the next. The important thing to watch is the trends over time. The Savvy trend reports are perfect for this and well worth the cost of the subscription.

https://apps.savvyaviation.com/flights/shared/flight/8944398/75270480-f077-4e40-9c9d-5b70f51d9a31

[hazek]

Thanks Rick, that was very good to see and learn from! Anyone else willing to share?