CHT again

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BlueYonder
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Re: CHT again

Post by BlueYonder »

There are a few other clues that timing may be an issue -- one that's gotten worse since I replaced the prop a few months back. I've got the shop looking at that right now, in fact.

I've brought this to the shop's attention today, and will have them look into it. Thanks for the input, everybody. This has bugged me for the 2.5 years I've had this plane, and it would be good to make another run at getting some answers.

I'm running it pretty darn lean. There's a lot of room to back that off, but I'm going to be burning quite a bit more gas.
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waynemcc999
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Re: CHT again

Post by waynemcc999 »

Sara, if you go even leaner of peak you will SAVE gas.
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astaib
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Re: CHT again

Post by astaib »

In my case I still have too hot CHT when I flight too low and too hot OAT. But it is not as hot CHT as you (400-415 max) in level flight.
Diamond Aircraft (Neil Grant) think that the Arizona Baffle will really help. I think that I will go for it.
When I fly higher or in winter time, my CHT are around 385.
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astaib
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Re: CHT again

Post by astaib »

If you lean too much the engine will vibrate (because not all 4 injectors have the same value, GAMI spread test) then each cylinder will shut down because to low fuel flow.
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perossichi
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Re: CHT again

Post by perossichi »

Sara

Your plane already has the Arizona cyl 1 baffle as it is a 2007.
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Re: CHT again

Post by BlueYonder »

waynemcc999 wrote: Wed Jul 10, 2019 8:12 pm Sara, if you go even leaner of peak you will SAVE gas.
I meant "back that off" to mean "run richer," which, no, will not save me gas. The choice is either to run richer and cooler, or lean it out further, run hotter....and save gas right up to the point where the engine chokes itself off (a state that's not a far reach from where I'm leaning it out to -- usually, another quarter-inch movement on the lean lever will get me there.)

I had the baffles replaced by Clay Lacy at BFI shortly after I got this plane, in an attempt to address the problem. No idea if they replaced it with this "Arizona" baffle y'all are talking about.
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waynemcc999
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Re: CHT again

Post by waynemcc999 »

Sara, if you have decently tuned injectors (have you run and recorded the GAMI test, and sent to GAMI for evaluation??):
-- as you decrease fuel flow beyond peak EGTs (the cyan lines on the MFD with the Lean button activated)...
-- you will see the EGTs (and after a time delay, the CHTs) decrease
-- you should then (depending on %power) shoot for EGTs about 50 below peak value (cyan lines) -- this will be your fuel flow setting for LOP operation (for a given power setting and density altitude)
-- if you decrease fuel flow even more, yes, eventually you'll run rough

See Mike Busch https://youtu.be/_VfiPuheeGw

Again, my guess is that when you lean you are still at or very close to peak EGTs (and therefore unacceptably high CHTs)... if you lean further to say 50 degrees Lean-of-Peak (assuming decently tuned injectors)... you'll both SAVE fuel and have LOWER CHTs.
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BRS
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Re: CHT again

Post by BRS »

astaib wrote: Mon Jul 01, 2019 7:11 am ...
One question: how do you do to be very accurate at 0.1 gph?
...
Astaib, The only way that I have found in order to get precise adjustment of the mixture (while testing) is to put a band around the Mixture latch to hold it open all the time. Don't forget to remove it once done testing.

We had to do this when developing the SuperCharger STC.
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Re: CHT again

Post by Scottsware »

My engine has just over 500 hours and I recently had both magnetos IRAN. The CHT seems to be running 10-20 degrees cooler.
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DaveS1900
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Re: CHT again

Post by DaveS1900 »

Sara,
I have fought a similar problem with another airplane, I feel your pain. Either there is no airflow to take the heat away (obstructions to airflow or airflow bypassing the cylinder baffles) or some thing is creating excessive heat (ie advanced timing or electronic ignition). You should do an experiment and post the results with the MP and mixture at various settings and record the CHT's.
Dave S.
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