EGT spread LOP vs ROP

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chocolatecake
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EGT spread LOP vs ROP

Post by chocolatecake »

When leaning if I go the ROP method the EGT always exhibits this pattern with #1 higher, 2&3 even, and 4 stepped down:
Image
Corresponding log:
Image

When going LOP I am able to get 1,2 & 3 pretty inline but #4 always stays lower:
Image
Log:
Image

CHTs always stay pretty tight and consistent, any ideas what might be going on?
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dmloftus
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Re: EGT spread LOP vs ROP

Post by dmloftus »

There will almost always be a spread on EGT's running ROP or LOP due to slightly different mixtures by cylinder. Suggest you read Mike Busch suggestions on checking GAMI spread between cylinders and, if needed, you might consider GAMI tuned injectors. Most IO360's, though, can run slightly LOP without GAMI injectors, usually creating more spread the further LOP you run. Also you want to avoid the Red Fin as Mike describes that can potentially destroy your engine. Difference in fuel flow is not the only thing that affects the EGT spread, and that's not really the most important thing to monitor. EGT sensor placement can influence the indicated temperature. You're really looking for where each EGT peaks and set your LOP point where you get the best balance of fuel savings and engine roughness. Also where you can maintain the best sustained CHT's.
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Re: EGT spread LOP vs ROP

Post by chocolatecake »

I did the GAMI injector check and it looks like there is a 0.6 spread, which seems pretty good. Is there a CHT you generally shoot for?
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Re: EGT spread LOP vs ROP

Post by mhoran »

Don't aim for a specific temperature, every engine is going to be different. Keep the CHT below 400, and lean out as you're doing. Your temps look great; I wish our CHTs were that tight. I wouldn't worry much about the EGT at all if the CHT is fine and the engine runs smooth. I wish I could get that low fuel flow without high temps. Maybe after our overhaul...
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Re: EGT spread LOP vs ROP

Post by waynemcc999 »

Scott, on the MFD capture of the LOP engine state... 22.3", 2290 rpm, 6.7 gph... I'm just curious why you're running at such a low power setting (~55% by my estimation)??

Seems you're either:
(a) at a pretty high density altitude (~14,000' DA), or
(b) not running at wide open throttle.

This is resulting in CHTs that, although very nicely balanced, are lower than what conventional wisdom now suggests (Busch suggests targeting 350-to-380) and further outside the "Red Fin" 65% than necessary. Even if you're at 14,000' DA, I'd still expect more like 130 KTAS (rather than 123 shown).
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Rich
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Re: EGT spread LOP vs ROP

Post by Rich »

waynemcc999 wrote: Thu Aug 04, 2022 5:51 pm Scott, on the MFD capture of the LOP engine state... 22.3", 2290 rpm, 6.7 gph... I'm just curious why you're running at such a low power setting (~55% by my estimation)??

Seems you're either:
(a) at a pretty high density altitude (~14,000' DA), or
(b) not running at wide open throttle.

This is resulting in CHTs that, although very nicely balanced, are lower than what conventional wisdom now suggests (Busch suggests targeting 350-to-380) and further outside the "Red Fin" 65% than necessary. Even if you're at 14,000' DA, I'd still expect more like 130 KTAS (rather than 123 shown).
I was curious about altitude as well and share that I normally strive for 350-380 CHT. But 22-ish in. of manifold pressure is WOT well below 14,000 ft. More like 8K.
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waynemcc999
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Re: EGT spread LOP vs ROP

Post by waynemcc999 »

Rich wrote: Thu Aug 04, 2022 8:04 pm I was curious about altitude as well and share that I normally strive for 350-380 CHT. But 22-ish in. of manifold pressure is WOT well below 14,000 ft. More like 8K.
Rich is of course totally correct on the manifold pressure... I was doing a horrible job keeping the various variables constant. I used my plane with WOT/2450rpm and 6.7gph to derive the 14,000' DA:
chart.png
... whereas Scott's example is ~2290rpm and logically significantly less than WOT.
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Re: EGT spread LOP vs ROP

Post by chocolatecake »

This was at about 4000' msl or 5500' DA. Definitely not WOT, had just leveled off and was cruising about 115KIAS because it was a quick 20 minute hop to a nearby airport.
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Rich
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Re: EGT spread LOP vs ROP

Post by Rich »

chocolatecake wrote: Fri Aug 05, 2022 2:22 am This was at about 4000' msl or 5500' DA. Definitely not WOT, had just leveled off and was cruising about 115KIAS because it was a quick 20 minute hop to a nearby airport.
For both flights then? It appears these were quite separate in time.
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chocolatecake
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Re: EGT spread LOP vs ROP

Post by chocolatecake »

Lean was on the way there, rich on the way back. Roughly 2 hours apart and same altitude.
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