EGT Span Question

[Rick_Luck]

The Grand Rapids Technologies 4000 EIS has and adjustable alarm for denoting when the difference between the lowest and highest EGT's exceeds a user defined limit. I've got mine set at 265. Over the years, I'd get an occasional alarm but lately it's been more frequent. In the cruise mode yesterday at a MP of about 24 or 25, I checked the EGTs several times and they were typically 1270 (left front), 1390 (right front), 1457 (left rear) & 1475 (right rear). Oil Temp was 160 and CHTs were 295, 331, 311 & 296 respectively. Later on, as I lowered MP slightly for a gradual descent, my EGT's came closer together at 1422, 1481, 1454, 1486.

I don't think I've got a problem and I've got an annual due in a little over a month, but my question is...If I have a compression issue in #1 cylinder, would the EGT go down or up? Intuitively, I'd think that the lower the compression....the lower the EGT, but then I also think I remember hearing somewhere that if a valve is leaking, the EGT goes up.

It's been a long time since I did any reading on engine operating characteristics & EGT's and I need a little refresher. When my EGT Span Alarm has gone off, by increase the leaning I've raised all EGT's but the #1 cylinder EGT would increase slightly more than the others to get the span within range to turn off the alarm. Before I spend too much time worrying about a possible problem, I thought I'd check if this might be one of those "quirks" that RV's can have.

Thanks

Rick Luck
RV9A N109RV
0-360D1A 275 hrs
const speed prop

 

[Geico266]

What engine are you running? Carb I assume?

 

[Rick_Luck]

I'm running an 0-360D1A. Carbureted.

I realize a carbureted motor would have higher EGT spans than a fuel injected one, depending on the efficiency (or evenness) of the mixture distribution via the intake manifold, but I don't know what is the normal range for the EGT's.


Rick Luck

 

[Steve Sampson]

Rick, in the cruise my EGT close right up, but in the climb they go far apart. There is a chart here. I suggest you double click it to be able to read it properly. You will see around a 300deg F spread, so if I had the same alarm, mine would also be going off.

I am no expert at this and use the blog as much as anything to capture what i think I know, and try to stimulate more feedback.

The thing that bothers me is that while we are told that actual EGT don't really matter, but changes do, its not totally true. What I do wonder is when a hot EFT is too hot. In some regimes I can drive them quite hot (if I wanted to) without the CHT going over 400.

I did share this data with Aerosport Power, and though they said it was a bigger spread than many they were not unduly concerned. I think the issue is that carb'd Lyco engines just have very poor fuel distribution.