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-   -   Did any attend Mike Busch's "Leaning the Right Way" forum? (https://vansairforce.net/community/showthread.php?t=162638)

Dean Pichon 07-27-2018 07:24 AM

Did any attend Mike Busch's "Leaning the Right Way" forum?
 
I attended the Tuesday session and like all his talks it was very interesting and informative. Later that day, it occurred to me that throughout his talk, during which he described how most any aircraft can run LOP, he never once mentioned that it was necessary to have a "GAMI spread" of some value (or less).

I had attended another talk at a previous Airventure, at which I recall Mike describing the importance of establishing a flow balance between each cylinder. It seemed odd that no mention was made of this during this session on how to lean.

Can anyone shed any light on whether this may have been an oversight, or perhaps it is only nice to do, but not required?

Carl Froehlich 07-27-2018 07:47 AM

I would assume not mentioning GAMI spread was just the way the discussion went - not some new insight.

On the RV-10 (stock Van?s IO-540-D4A5) the GAMI spread started out well over a gallon per hour on the first LOP test. The engine was simply not happy as reflected in it running very rough. It took just three runs to identify which injector nozzles needed to be replaced and by what value. Four nozzles swapped out ($26 each from Air Flow Performance) and GAMI spread is consistently 0.1 gph. LOP operations are now smooth, even further into LOP than is practical.

I consider tuning injector nozzles to get GAMI spread below 0.3 gph a hard requirement for any RV. Why abuse your engine when it is so easy to do this?

Carl

rightrudder 07-29-2018 04:22 PM

I was lucky. Did GAMI spread testing to see if I could improve over factory nozzles, but spread was right around 0.5 gph. Close enough for me.

roadrunner20 07-29-2018 04:44 PM

I attended that forum & he did mention the GAMI spread.
There was a pilot with a IO-550 waiting to get his GAMI injectors and was concerned on the timing of his cylinders peaking. Mike said the whole idea with the spread is to manage the fuel flow & close the timing gap of the cylinder achieving their peak.
If I understood it correctly.

Dean Pichon 07-29-2018 04:57 PM

Quote:

Originally Posted by roadrunner20 (Post 1276822)
I attended that forum & he did mention the GAMI spread.

Must be I missed that part! Two years ago, I attended another of his forums that was specifically on flow balancing. I went home and installed an engine analyzer and found my cylinders were reasonably well balanced (~0.2-0.3 gph depending upon altitude).

This morning I went for a flight and ran LOP for the first time. It seemed to work well enough and significantly reduced my fuel flow. I did, however, find that the number one cylinder was running much cooler than the hottest, so I may need to do some further balancing.

My issue now is that my cylinders are running too cool. This morning, they only reached ~280F when running LOP. Typically, they are about 320F. I will experiment with running a bit less lean.

lr172 07-29-2018 08:01 PM

Quote:

Originally Posted by Dean Pichon (Post 1276829)
My issue now is that my cylinders are running too cool. This morning, they only reached ~280F when running LOP. Typically, they are about 320F. I will experiment with running a bit less lean.

And what damage or problems do you expect might be caused by running at 280 vs 320 CHTs?

Larry

Dean Pichon 07-30-2018 06:18 AM

Quote:

Originally Posted by lr172 (Post 1276870)
And what damage or problems do you expect might be caused by running at 280 vs 320 CHTs?

Larry

Good question. One of the Mike's leaning videos posted to YouTube indicated that at temperatures below 300F, the valves are more likely to accumulate deposits. I don't have much to go on, though.

49clipper 07-30-2018 10:45 AM

49clipper
 
My cylinders run much cooler than 300f a lot. According to Lycoming, I am lucky and they said my cylinders should last til TBO. He said, call me when they get below 175f and we'll talk. Cool cylinders are a plus not a problem.
Jim

rvanstory 07-30-2018 11:27 AM

In his book, and on my Savvy reports, Mike says a .5 spread is the acceptable GAMI spread limit for smooth LOP operations.

lr172 07-30-2018 11:35 AM

Quote:

Originally Posted by 49clipper (Post 1276981)
My cylinders run much cooler than 300f a lot. According to Lycoming, I am lucky and they said my cylinders should last til TBO. He said, call me when they get below 175f and we'll talk. Cool cylinders are a plus not a problem.
Jim

This was my understanding as well. You want the heads as cool as possible. Water cooled engines are running comparable CHTs under 200* 180-200 is the sweet spot. Much less and you give up a bit of combustion efficiency. You do need enough combustion heat to keep lead deposits from forming. However, unti someone publishes correlated charts that show CHTs related to combustion temps and cooling airflow, I don't know how we use CHTs to ensure we are above the critical temps, beyond trial and error. My speculation is that at any meaningful RPM, no matter how far LOP, we are well above that temp. In our world, it is the low temps at the 1000 RPM area that do not create enough heat to convert the lead to lead bromide (this conversion eliminates the deposits).

Larry


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