I'm pretty old school....
I lean my 470 by the same routine as glacier describes.
I have a standard single point CHT gauge & no EGT.
I would like a multi-point CHT gauge & will get one at some point,
certainly when I get my high-time engine overhauled if not before,
but I'm not convinced I need an EGT gauge for a carburated engine.

I can use either of the three leaning techniques on my O-300 and they all get me the same results. 1. Lean till rough, enrichen till smooth. 2. Shut one magneto off, lean till rough, turn both magnetos on. 3. Use lean find mode on my engine monitor.

I can also just lean by fuel flow or two inches on my mixture level and be within probably 10% of the correct setting just by feel/sound.

I love having an engine monitor for analysis and maintenance trouble shooting, but I don't think it is needed for ROP operation of a carbeurated engine.

hotrod180 wrote:I'm pretty old school....
I lean my 470 by the same routine as glacier describes.
I have a standard single point CHT gauge & no EGT.
I would like a multi-point CHT gauge & will get one at some point,
certainly when I get my high-time engine overhauled if not before,
but I'm not convinced I need an EGT gauge for a carburated engine.

I find the real benefit of a fully instrumented engine is diagnostics. It’s akin to diagnosing a car with a OBD2 code reader vs without.

Having fuel flow offers the biggest benefit while operating the engine, IMO. I set the fuel flow according to the factory power charts and my engine is happy. Plus, I know exactly how much fuel I have available.

Agreed, I posted some time earlier this year asking about whether or not an engine monitor was any use on a carbeurated 470, and my experience in the few flights I've made so far match the consensus - you're definitely not going to gain anything over the tried and true methods in terms of leaning... but the additional data for troubleshooting is valuable.

Thanks everyone for the input!

An engine monitor that strikes a balance between too much information (TMI) and valuable insight is money well spent, I'm still search for just such at sweet spot.

whee wrote:....I find the real benefit of a fully instrumented engine is diagnostics. It’s akin to diagnosing a car with a OBD2 code reader vs without. Having fuel flow offers the biggest benefit while operating the engine, IMO. I set the fuel flow according to the factory power charts and my engine is happy. .....

I'm curious what extra diagnosing can be done with both an EGT & a CHT, vs just a CHT?
Seems like the EGT is mainly for leaning.
Fuel flow seems to be a pretty big deal for injected engines,
but I don't know that I've ever seen a specified fuel flow range for a carbureted 470.
My thoughts are to install a 6 point CHT, & perhaps also a digital oil temp / oil pressure gauge,
and put them both on the far left side of my panel.
Leave the ammeter & the (backup) mechanical oil pressure gauge over on the RH side.
That way all my critical flight and engine instruments would be on the LH side of the panel, in my primary scan.

CParker wrote:Thanks guys, I'm very familiar with the articles by Deakin and Busch (seems his webinar is basically reading off Deakin's article)... my question isn't about leaning itself, just where you guys find that an O470 starts to complain relative to peak EGT when leaning in a normal cruise situation.

Yep. Busch attended one of the early versions of the "Advanced Pilot Seminar" developed by John Deakin, George Braly, and Walter Atkinson (recently deceased).

In that APS seminar, they teach a lot of stuff that isn't in the engine and POH manuals (including the reasons it's not in the manuals). They believe that understanding how the engine actually works, and learning the indicators of various conditions (some benign and some extremely dangerous) are the keys to operating your aircraft engine for longevity. They teach the differences in operating rich-of-peak and lean-of-peak mixtures in your engine. The explain when and why each of those techniques has validity, and the conditions where it is safe to use both techniques. More importantly, they explain why... in a way that makes absolute sense, and is backed by empirical testing data from an instrumented engine lab.

Mike's approach is different. He is teaching much of the same information, but by using some "rules of thumb" about operating your engine. This concerns the APS guys a bit, because what works in one situation might not work in another, and while the APS guys teach the "how to recover when something goes wrong," Mike tends to just ignore that aspect of the teaching / training. In fairness, Mike's seminars are one-hour time slots, versus the two days allocated for the APS course.

It's mostly a difference in philosophy: Mike is handing out fish for people to eat right now, whereas the APS guys are teaching people how to fish for themselves. Long term, there's a lot more value in learning to interpret the engine monitor's readings for various purposes (including some advanced diagnostics) than there is in simply learning one "trick" to use.

All that said, BOTH of these sources agree that absolute EGT readings (except for the limited case of turbocharged engines, where there may be specific EGT limits based on the metallurgy of the exhaust pipes) are meaningless. EGT readings are an inexact science at best. The same cylinder on the same engine can have two different probes installed in the exact same position whose readings differ by a significant margin.

Likewise, the same probe inserted an inch upstream or downstream from the original position will read significantly lower or higher that it does in the original position. Even just installing the probes facing one direction versus the other can cause different readings from that same probe.

But none of that really matters. What DOES matter is the difference between the current EGT reading, and the "peak" EGT reading for that particular cylinder. Are you richer or leaner than "peak" EGT, and by how much? There's a ton of articles on that topic (including several in Deakin's "Pelican's Perch" series) that discuss this, so I won't go into it here... PM me if you want more info.

hotrod180 wrote:I'm curious what extra diagnosing can be done with both an EGT & a CHT, vs just a CHT?
Seems like the EGT is mainly for leaning.

CHT is a "lagging" instrument. It takes a while for the effects of anything that takes place inside the cylinder to become visible via CHT. For instance, let's assume you develop an intake leak on one cylinder, so that it is running noticeably leaner than the others (excess air, right?). Your fuel flow is the same as usual, and the engine isn't running rough – at least not at first... By the time the excess heat in the cylinder head finally causes the CHT on that cylinder to rise enough for you to notice it is approaching the danger zone, even going to full rich may not be enough to reverse the trend so as to prevent or stop pre-ignition (caused by "hot spots" in the cylinder igniting the fuel/air mixture before the plugs fire) – which would likely destroy at least that one cylinder.

By contrast, EGT is nearly instantaneous. A leak such as the above would result in significant rise in just that one cylinder's EGT. A fouled plug likewise shows up almost immediately. EGT "excursions" from the normal baseline established on previous flights.

Flying based solely off CHT is kind of like using your bank statement from last month to determine if you can write a check on your bank account. It shows "past history" as reflected in the thermal energy transmitted into the head, versus what's happening "right now" shown via the exhaust gas temps.

(That's a bit over-simplified, but should give you the general rationale for EGTs being as important as CHTs for day-to-day operation, and far more important and useful for diagnostics.)

That makes sense-- thanks, JP.