Another lean of peak question

[n86121]

The logical time to put in an engine analyzer will be during annual when the other things are being done. I just came out of annual, so it will be a while, unless I decide to ground the airplane for a few weeks at least.

For 25+ years I've run my turbo 337 ROP at 75% around 100F ROP. All has been fine.to get

I have a dual engine SHADIN (feeds the avidyne IFD).
I find the leaner engine and richen it to 100F.
Then make the richer one match that, the same fuel flows and keep my fuel math simple.
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TCM in video and documents say that you cant hurt your engine at 65% or less no matter how much you lean.

I already have GAMI in front and rear (last annual).

So for an upcoming trip I could

OPTION A. Continue fast at 75% 100F ROP,
as I have for years, or

OPTION B. Slow a bit, at 65% or less and LOP until engines (w GAMI's) start to wobble,
then richen a hair. Remember, according to all sources, no detonation below 65%.

Keeping an eye on my single CHT for each engine.

What are the risks, if any?

What say you all?

[edasmus]

My research agrees with your logic. I fly for entertainment and rarely have anywhere to go. My plane is not turbocharged but I have always set 65% or less in cruise and lean to my heart’s content. I’ve owned my plane since 2002 and flew my last set of factory engines about 400 hours past TBO. I overhauled at Poplar Grove in 2020 and 2021 on the front then rear respectively.

The front engine did develop a cylinder problem on #5 that ultimately inspired my choice to overhaul. I could have repaired however my engines were 30 years old so I decided that was long enough without looking at everything.

I overhauled the front at that time and other than #5, all was well. I retired the rear engine a year later and all was well with that engine also. Both engines are now recently overhauled with factory new cylinders on both.

I now intend to go another 30 years if I live that long. 😉😂 My airplane does live in a fully insulated heated and air conditioned hangar which I’m guessing doesn’t hurt. In my experience, set 65% or less and run those red levers wherever you want to. It’s the equivalent of “babying” your engines. Assuming the engines are mechanically sound and rigged correctly, they’re simply not making enough power to hurt themselves at that low power setting. At higher power settings, the story is different especially in your turbocharged engines.

The only other thing I can think to add is my buddy’s experience in his T210 which he’s owned about 11 years now. He fly’s all around the country in his plane frequently in the high teens. His experience has been vastly different. His plane is fully equipped with one of the fancy engine analyzers/recorders. He’s extremely attentive to engine management yet in 11 years he’s had cylinder work on 5 of 6 cylinders. His engine was about mid time when he purchased and it’s about at TBO now (1400 or 1500 ish). The only thing we can attribute the cylinder issues to is either the first half of the engine’s run by the previous owner was NOT done attentively or turbocharged engines simply are harder on cylinders. I can say his head temperatures are always warmer than mine. Mine settle on 300-320 on front and 340-360 on rear. He’s always managing to not exceed 380 and does see 400 in the long slow climb to the high teens. Maybe that’s the difference. 🤷*♂️ His plane lives in an identical hangar as mine except without the A/C.

He’s approaching overhaul time with his engine so it will be interesting to start with a fresh engine but it’ll be years before we actually have the data to make the comparison.

Good luck and your mileage may vary. 😊

[n86121]

From my excruciating review of TCM manuals,
interlaced into T337D performance charts...

75% ROP will give around 150knots IAS @ 13.3gph (ea) x2 = 26.5 gph
65% LOP will give around 140knots IAS @ 10.3gph (ea) x2 = 20.6 gph

In the turbo, (non-pressurized) TAS increases linearly @10 knots/5k ft

Until you hit 25k (critical altitude), when engine poer starts to dropoff
I've never taken it that high, that's a looooong way down if you want to stop!

So for example, at 10k ft

TAS 75%= 150+10x2=170k @ ROP = 26.5.3gph = 6.4 kn/gal
TAS 65%= 140+10x2=160k @ LOP = 20.6gph = 7.7 kn/gal

= 20% more range/gal = 6% reduction in TAS speed.

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Applied to my theoretical 1400 kn trip (each way) from Wash DC to Denver and back... 2800 miles total...

75% = 2800/170k = 16.5 hrs @ 26.5 = 440 gals
65% = 2800i/160k = 17.5 hrs @10.3 gph (ea) =360 gals

For ~80 gals extra (roundtrip ~$500?) ...I can cut the round trip time by just ~1 hours...?

Questions become,

1) Am I willing to pay $500 to get an hour of my time back? ...nah, I'll just enjoy the cruise for another hour

2) If the airplane costs $200/hour (??), one less hour reduces the extra fuel cost by $200....

CONCLUDE => It does seem to suggest LOP at 65% and enjoy the extra hour of flight time...

Thoughts?

[edasmus]

"Excruciating".... YEP

You have summed it up! In my senior years, I've reduced the story to a much shorter version.

Higher POWER = Higher SPEED = Less TIME = More $$$ (In FUEL and probably MAINT.)

Lower POWER = Lower SPEED = More TIME = Less $$$ (In FUEL and probably MAINT.)


It's not black and white however in my opinion. There are infinite shades of gray and countless variables go into the longevity (or lack there of) of our engines. Heck, many variables we cannot even control. We simply do the best we can and continue learning all the time. It's part of the fun I suppose.

Enjoy your flight. Bring a pee bottle. I'd hate for you to have to heat up your engines just to make it to the little "pilot's" room. ;o)