Help me solve my CHT limited climb performance

[FasGlas]

Just another two cents thrown in. When talking about the temps of the cylinder, consider where we take the temp reading. Mostly deep in the head or some use the spark plug ring, but both at the least point of cooling. While this is the customary location to get the readings, it's not the temp of the entire cylinder. I might be wrong but I would think these are the hottest points of the cylinder, not the temp of the entire cylinder. To know if you're glazing the hone lines you'd have to measure the barrel temps and to know if you're breaking down the molecular structure on the metal you'd have to measure the temps of the entire cylinder, not just the hottest point.

The same applies to the oil temps. The oil in the sump is far hotter then the oil temp reading at the oil filter adapter. This oil can be as much as 40 degrees hotter.

[RV7Guy]

Originally Posted by rzbill

I agree with the other poster that Mike Busch is probably the main source of the 400 degree limit.

To RV7Guys point, our engines have been well developed and obviously have iterated to designs that accommodate aluminum at less than peak strength since many engines have operated above 400 F for their whole life. The temperature limits noted by Lycoming would prevent strength loss below a certain value (whether by design or experience) that they feel is acceptable.

I choose to do everything I can to keep them as cool as possible.

Don't get me wrong, I'm without question an advocate of keeping as cool as possible. But, the reality of it is it is nearly impossible to operate below 400 in a climb in central AZ. Unless, of course you want to use the curvature of the earth as your climb rate.

I appreciate Mike Busch's information. I went right to the source of the engine, ECI, and learned that there is absolutely nothing wrong with breaking 400 as long as it is transient. Again, this is just reality here.

Personally, I use 420 as my limit and adjust climb rate for reduced temps at that point. I have taken off to fly to work at 117 ramp temperature. I was at 400 for the 12 minute flight to work at 3000msl at a very moderate power setting.

Yes, keep them cool but don't panic or avoid a flight because the CHT's might hit 400.

[David-aviator]

Originally Posted by db1yg

Hey David,

Did you see any change in cruise speeds before/after the mod.???

Cheers,

db

Have no data to answer your question. If there is a change it is not much.
Cooling comes at a cost.

[java]

Originally Posted by RV7Guy

Don't get me wrong, I'm without question an advocate of keeping as cool as possible. But, the reality of it is it is nearly impossible to operate below 400 in a climb in central AZ. Unless, of course you want to use the curvature of the earth as your climb rate.

I appreciate Mike Busch's information. I went right to the source of the engine, ECI, and learned that there is absolutely nothing wrong with breaking 400 as long as it is transient. Again, this is just reality here.

Personally, I use 420 as my limit and adjust climb rate for reduced temps at that point. I have taken off to fly to work at 117 ramp temperature. I was at 400 for the 12 minute flight to work at 3000msl at a very moderate power setting.

Yes, keep them cool but don't panic or avoid a flight because the CHT's might hit 400.

On a related note, prior to my panel upgrade I had an analog CHT gauge with a four way switch, reading from spark plug ring sensors. CHT's would get to about 400 but not above, even climbing at Vx on warm days. Now with a digital readout and probe sensors I regularly see 420+ climbing much less aggressively. How many aircraft (RV's or otherwise) regularly go into the 400's without knowing due to inaccurate instrumentation, yet don't have engine problems?

[DanBaier]

I just helped a friend install some cooling louvers (http://www.aircraftspruce.com/catalo...clickkey=26849) on the bottom of each side of the cowl (O-360 with FP prop). CHTs were the problem, much as OP described - oil temp was not. CHTs dropped about 40 degrees at the loss of about 1-2 knots.

Not necessarily the solution for everyone, but in this case it worked well.

Dan

[aerhed]

I thought it was well known that bayonets read around 25 degrees higher than plug gasket TCs.

[DanBaier]

Actually, I've heard it the other way around - the plug gaskets read something like 50 higher than the probes in the cylinder.

Dan

[FasGlas]

Originally Posted by DanBaier

Actually, I've heard it the other way around - the plug gaskets read something like 50 higher than the probes in the cylinder.

Dan

Yes, I believe that's right. It picks up extra heat. But I don't recall it being as high as 50, more like 20.

[MauiLvrs]

Originally Posted by DanBaier

I just helped a friend install some cooling louvers

We considered that option and instead opened up the exit area 5/8" instead.
Temperature drop was in excess of 30 degrees.

[Toobuilder]

A question for you guys opening up the cowl exit or adding louvers:

Are you getting this dramatic temperature drop across the entire operating range, or primarily in the climb?

Both the -8 and Rocket run plenty warm in climb, but are now too cool in cruise... Seems that the opened cowl exit would only make that situation worse.