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07-27-2018, 07:24 AM
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Join Date: May 2006
Posts: 532
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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?
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07-27-2018, 07:47 AM
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Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,597
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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
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07-29-2018, 04:22 PM
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Join Date: Mar 2014
Location: Laguna Hills, CA
Posts: 1,805
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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.
__________________
Doug
RV-9A "slider"
Flew to Osh in 2017, 2018 & 2019! 
Tail number N427DK
Donation made for 2020
You haven't seen a tree until you've seen its shadow from the sky -- Amelia Earhart
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07-29-2018, 04:44 PM
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Join Date: Feb 2005
Location: Bay Pines, FL (based @ KCLW)
Posts: 1,955
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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.
__________________
Danny "RoadRunner" Landry
Morphed RV7(formally 7A), N20DL, PnP Pilot
1190+ hours
2019 Donation Paid
Last edited by roadrunner20 : 07-29-2018 at 04:56 PM.
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07-29-2018, 04:57 PM
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Join Date: May 2006
Posts: 532
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Quote:
Originally Posted by roadrunner20
I attended that forum & he did mention the GAMI spread.
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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.
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07-29-2018, 08:01 PM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Quote:
Originally Posted by Dean Pichon
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.
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And what damage or problems do you expect might be caused by running at 280 vs 320 CHTs?
Larry
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
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07-30-2018, 06:18 AM
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Join Date: May 2006
Posts: 532
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Quote:
Originally Posted by lr172
And what damage or problems do you expect might be caused by running at 280 vs 320 CHTs?
Larry
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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.
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07-30-2018, 10:45 AM
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Join Date: Dec 2006
Location: Belleville
Posts: 306
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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
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07-30-2018, 11:27 AM
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Join Date: Dec 2016
Location: New Braunfels
Posts: 299
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In his book, and on my Savvy reports, Mike says a .5 spread is the acceptable GAMI spread limit for smooth LOP operations.
__________________
Randy Vanstory
Flying RV10 - N783V
1st Flight 08/20/2020
Donation Happily Made 2020
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07-30-2018, 11:35 AM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Quote:
Originally Posted by 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
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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
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Last edited by lr172 : 07-30-2018 at 11:50 AM.
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