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Significant EGT, CHT Difference Between C1/C2 and C3/C4

ssokol

Well Known Member
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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?
 
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.
 
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
 
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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.
 
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?
 
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.
 
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.
 
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.
 
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.
 
I would recommend getting a hold of a thermocouple calibrator. I have built an engine monitor and find my design is accurate to nominally 2 degrees on K-type thermocouple inputs but in some temperature ranges it can be off a few more. The calibrator I have is an Altek 322-1.
 
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?


VERRRRRRYYYYY interesting...I also have an RV9A with the identical problem. I bought this RV two weeks ago in Yakima WA and flew it back home to Lancaster, SC 2600 miles. The two rear cylinders had lower CHTs by a bunch and lower EGTs by a bunch. I had to lean the front two cyl to peak and more just to get the back two acting somewhat right. Today after checking the plugs in the rear two cyl, I found #4 VERY sooty and #3 very dark, and the front two just right. I pulled the injectors from all cylinders and put the outputs in four small containers, then ran the boost pump with throttle in and full rich mixture. After about a minute. The pump was stopped and levels checked. The results confirmed the EGT/CHT values I was seeing...#4 which had the lowest EGT and CHT had nearly 50% more fuel in the container that either #1 or #2 and #3 had maybe 25% more fuel that the front two. This correlates exactly to the temps I see and the plug color evidence. I have exchanged injectors with cylinders and find the flow stays with the cylinders? I have also checked the injector sizes and all are the same.

I am very confused. How could the flows be different to the cylinders when the spyder is just a manifold, supplying the same pressure to each line and each injector? :confused:

Ed Lee
RV9A
IO-320 160 hp
 
EGT/CHT significant difference

I forgot to add to my post above that I have the Airflow Performance system.

Ed Lee
 
I am very confused. How could the flows be different to the cylinders when the spyder is just a manifold, supplying the same pressure to each line and each injector? :confused:

Ed Lee
RV9A
IO-320 160 hp

partial blockage for two of the ports inside the spider. It is not just a manifold. Each individual output has a small v shaped slot for metering fuel. I would expect to see small debris creating blockage near the upper part of the V in two of them (cyl's 1 & 2).

Larry
 
Fixed!

partial blockage for two of the ports inside the spider. It is not just a manifold. Each individual output has a small v shaped slot for metering fuel. I would expect to see small debris creating blockage near the upper part of the V in two of them (cyl's 1 & 2).

Larry

Larry, you are spot-on. Did a flow test to prove what was happening, then removed flow divider and flew down this morning to Airflow Performance. They flow tested it on their flow bench and confirmed my tests, then removed the top and back flowed it and found a small metal chip that probably came from the recent installation of the system. Reassembled and tested and found it perfect. Then Don at Airflow asked what primer restrictors I had (bendix system) and I told him, one band, therefore .028. He said that is too large for an O-320 and gave me 4 .022 restrictors. Came home and flew it and it is amazing what the engine does. All cylinders peak at the same time and for the first time I could run LOP with perfect smoothness.

These guys at Airflow Performance are the best! They work on their own systems and also Bendix systems and are an authorized repair station for Bendix. The great thing is they are only 80 miles from me in Spartanburg, SC (KSPA). Don, Kyle, Warren, Mark, Colleen, the most helpful, knowledgeable people in business I have known.

Ed
 
Larry, you are spot-on. Did a flow test to prove what was happening, then removed flow divider and flew down this morning to Airflow Performance. They flow tested it on their flow bench and confirmed my tests, then removed the top and back flowed it and found a small metal chip that probably came from the recent installation of the system. Reassembled and tested and found it perfect. Then Don at Airflow asked what primer restrictors I had (bendix system) and I told him, one band, therefore .028. He said that is too large for an O-320 and gave me 4 .022 restrictors. Came home and flew it and it is amazing what the engine does. All cylinders peak at the same time and for the first time I could run LOP with perfect smoothness.

These guys at Airflow Performance are the best! They work on their own systems and also Bendix systems and are an authorized repair station for Bendix. The great thing is they are only 80 miles from me in Spartanburg, SC (KSPA). Don, Kyle, Warren, Mark, Colleen, the most helpful, knowledgeable people in business I have known.

Ed

Glad you figured it out. Don and kyle are tops in my book also.
 
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