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  #1  
Old 05-07-2020, 12:26 PM
ssokol ssokol is offline
 
Join Date: Jan 2016
Location: Cupertino, California
Posts: 121
Default Significant EGT, CHT Difference Between C1/C2 and C3/C4

In the process of testing out my engine monitor (the one I'm building) I ran a detailed log of a flight which captured some interesting facts. Turns out that there's a significant difference in both EGT and CHT between the two forward cylinder and the two aft. Engine is an IO-320 160 HP.

Max EGT Values: 1042.52, 1106.60, 1408.28, 1403.06

Max CHT Values: 322.70, 358.52, 386.42, 379.22

I fully expected the cylinder head variance due to basic airflow, but I'm quite surprised to see that the max exhaust gas temps vary that much.

Note that those are the maximum temp values over the course of a 45 minute flight, sampling at 10 Hz. The averages show much the same:

Avg EGT Values: 870.57, 946.65, 1174.19, 1187.25

Avg CHT Values: 288.47, 317.31, 335.30, 337.83

Does that seem normal, or is there something odd going on here?
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  #2  
Old 05-07-2020, 12:30 PM
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Raymo Raymo is offline
 
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Location: Richmond Hill, GA (KLHW)
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Default

Probably not possible to derive anything from the numbers unless you know the GAMI spread. I suggest you upload your data to the Savvy website for review. Probe placement may also be involved with the variation in EGT.

Here is a link on how to perform the test flight profile for analysis.
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  #3  
Old 05-07-2020, 02:29 PM
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OZCleco OZCleco is offline
 
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Location: Maylands, Western Australia
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Default

Snapshot figures of EGTs are basically meaningless. For comparing between cylinders measure the difference between full rich EGT and absolute peak EGT for each one.

Your maximum CHTs look great but what was the ambient temp?

As a complete system I'd question the balance between fore and aft temperatures. Why are the forward cylinders cooler relative to the cylinder behind? Are they robbing most of the cooling air or is there too much/not enough air escaping in the rear? What is the integrity of the plenum pressure vessel?

In general, how is the air being controlled through the cowling?

Walking up to your engine my attention would be drawn to your oil cooler location, the baffle gap behind C3, the ramps (if any) ahead of C1/C2, the mid point of your C1/C2 cylinder barrels relative to the inlet ramps, the state of your upper baffle seals, any tell tale signs to indicate how your baffle seals were last sitting, (i.e. the wear marks on your baffle seals and your top cowl), inlet ramp seal placement with the cowling installed, depending on aircraft model the integrity of the lower cowling carby inlet seals, the integrity of your lower baffle wraps, the lower cowling exit area, etc.

Only then would those CHTs mean anything to me.

*edited for spelling

Last edited by OZCleco : 05-07-2020 at 02:31 PM.
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  #4  
Old 05-07-2020, 08:25 PM
Boyd Birchler Boyd Birchler is offline
 
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Location: IN
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Looks like #1 and #2 are way too rich and #3 and #4 are just right. I would swap #3 and #4 injectors with injectors #2 and #1 and see if the low EGT's follow. If they do not follow you need to size down the injectors on #1 and #2.
If they do follow, those two injectors with the low EGT's might be different in size from the other two.

You can talk to Airflow Performance. If you are lucky you will have the style of injectors with inserts. The inserts are easy to change for tuning to get proper EGT's. Otherwise you may want to change to that style.

In a perfectly balanced engine all EGT's go over peak,as you continue to lean, at the same fuel flow. That way you don't have one way too lean and the other three way too rich. The lean one in that case dictates that you stop leaning and the other three are burning way too much fuel.
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  #5  
Old 05-07-2020, 08:41 PM
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Mike S Mike S is offline
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Steve, did you have any data from your prior setup??

Do the readings with the new instrumentation follow the old data----if you have any?
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  #6  
Old 05-07-2020, 09:13 PM
Kyle Boatright Kyle Boatright is offline
 
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Are all 4 EGT sensors the same distance from the exhaust/cylinder flange?
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  #7  
Old 05-07-2020, 09:21 PM
sjhurlbut sjhurlbut is offline
 
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Default EGTs

I had a EGT spread on my engine also. Firstly verify the wiring. I had a pinched (very minor on connector back of engine monitor) EGT causing increased resistance. This caused my EGT to drop by 400 deg. Sounds pretty close to your problem. That big difference would be a lot of fuel imbalance.
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  #8  
Old 05-07-2020, 10:28 PM
lr172 lr172 is offline
 
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Something is going on. Best to verify the instruments first. Swap egt sensors front to back to confirm readings. 300-400* is a big egt spread, assuming a constant installation distance from flange.
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  #9  
Old 05-08-2020, 11:31 AM
ssokol ssokol is offline
 
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Location: Cupertino, California
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Default Not necessarily a new issue...

I've had this RV for about three years now and it's always had something of a spread between the forward and aft jugs. The Dynon which I was using until last year showed something of a spread, but to be honest I didn't pay that much attention as the probes where old and one only worked intermittently.

When I replaced the Dynon with FlightView last summer I put in all new probes. In looking back through the (rather limited) data I've collected it appears that this has been an issue all along.

I'm confident it's not the probes. Since I'm using this as a shakedown of the EMS data acquisition system, I did a lot of tests with the probes prior to installation to make sure that they were working. After installation I did a good bit of testing to make sure the wiring (all proper thermocouple wire) didn't have an impact on accuracy.

Probe placement is a possibility. I don't know if there's a difference between the fore and aft probe sets. Next time I pull the cowl I'll check.

The engine was built by Aero Sport Power. I may check with them to see if they have any thoughts. They may have some record of what injector nozzles they used.
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  #10  
Old 05-08-2020, 11:39 AM
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Mike S Mike S is offline
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If this was only a CHT issue, I would suggest the air dams in front of cyl 1 & 2-----and although they may still be a part of the problem, they will not account for the EGT imbalances.

But----check to see if they are there. It is possible you have two issues going on.
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