EGT or not to EGT...that is the question

[JDanno]

Is EGT important in an alternative engine setup using a LS1 engine or a Subaru? The fuel is controlled by the throttle and the ECU so that there is no lever for mixture.
How about using CHT only? Since you can't vary the mixture it would seem that CHT would be the only temperature measurement that would be useful.
Inquiring minds want to know!

[DGlaeser]

I have coolant temp, not CHT. Not sure what CHT tells you for a liquid cooled engine.
I don't have EGT either. I don't have a way to control it so it would be informational only.
On my list of things to do is add the equipment (from the ECU manufacturer - SDS) to be able to adjust mixture. They recommend using Air/Fuel ratio as the criteria, which means addiing an O2 sensor. I plan to add EGT as well, since it's easy, but it would be secondary info since AFR would be primary for adjustments.
In summary the engine parameters I monitor are:
Coolant temp
Oil Temp
Oil Pressure
GB Temp
Fuel Pressure
Fuel Flow (uses injector pulse - very accurate)
Manifold Pressure
RPM (I use Prop RPM, some use engine RPM)
Volts (not really an engine parameter, but it is an electrically dependent engine )

[Mike S]

I would think it would be an important indicator of whether the ECU is doing its job.

[John Clark]

Originally Posted by Mike S

I would think it would be an important indicator of whether the ECU is doing its job.

I agree. Although you never see a CHT on the engines mentioned in their original, automotive installation, there have been plenty of stories of ancilliary system failures in aircraft applications. I would instrument all sorts of things at least through the engineering and test flight stage. I recall one rather costly ECU caused meltdown in an RV10 Chevy V8 installation. In the case of a liquid cooled engine, I would want several coolant temperature probes to determine that the coolant was flowing properly.


John Clark ATP, CFI
FAA FAAST Team Member
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA

[JDanno]

How would you go about "probing" for prop RPM on a P.S.R.U (like most all Alt. engine) equipped plane?
I would think you would want both engine and prop RPM info.
The CS props would also have this problem. I'm not sure where its instrumented. Thanks!!

[JDanno]

Well, I would dearly love to buy a SDS system but they aren't doing anything for the LS1. Anybody else out there doing something similar? I'm asking all kinds of questions as I'm at the stage of my install where I need to know this. Thanks again. Dan

Originally Posted by DGlaeser

I have coolant temp, not CHT. Not sure what CHT tells you for a liquid cooled engine.
I don't have EGT either. I don't have a way to control it so it would be informational only.
On my list of things to do is add the equipment (from the ECU manufacturer - SDS) to be able to adjust mixture. They recommend using Air/Fuel ratio as the criteria, which means addiing an O2 sensor. I plan to add EGT as well, since it's easy, but it would be secondary info since AFR would be primary for adjustments.
In summary the engine parameters I monitor are:
Coolant temp
Oil Temp
Oil Pressure
GB Temp
Fuel Pressure
Fuel Flow (uses injector pulse - very accurate)
Manifold Pressure
RPM (I use Prop RPM, some use engine RPM)
Volts (not really an engine parameter, but it is an electrically dependent engine )

[rv6ejguy]

EGT is pretty useful for diagnostics and somewhat useful to monitor basic air/fuel ratios (AFRs) if you are running leaded fuel. Wideband O2 setups are the best way to get ECU tuning correct but leaded fuel is unfriendly towards the sensors. Some people have had decent luck with the sensor life by using Decalin lead scavenger and extensions to the O2 sensor mounting boss to prevent direct impingement of the lead in the exhaust stream from accumulating on the sensor element.

CHT is not very useful in a liquid cooled engine. Of more use would be at least two water temp sensors, one for outlet from the engine and one for outlet from the radiator. You want to monitor all the usual stuff as well as gearbox temp and volts. Lots of gauges/ probes are good for initial testing and development. I've got ins and outs on almost everything on my RV10.

Engine rpm is important to know and you could add a Hall Effect near the prop flange if you wanted prop rpm. Certainly nice to know both, especially for initial governor and pitch stop setup.

For tuning, keep the AFRs richer than 13 to 1 at WOT. If you still have the cast pistons in there, beware that GM runs around 11 to 1 on the factory ECUs to keep the pistons alive after about 30 seconds of WOT and RPM above 4000. Go one heat range colder on the plugs, watch total ignition advance carefully on 91 octane and try to keep EGTs under 1400F. If you are using a crate engine, use the recommended thin Mobil 1 oil as the bearing clearances are often on the tight side on these engines and they have been known to spin bearings after many minutes of WOT/ high rpm running.

[DGlaeser]

Originally Posted by JDanno

How would you go about "probing" for prop RPM on a P.S.R.U (like most all Alt. engine) equipped plane?
I would think you would want both engine and prop RPM info.
The CS props would also have this problem. I'm not sure where its instrumented. Thanks!!

A tach pulse is typically taken from the ignition - either the ECU or magneto depending in the engine. Prop and engine RPM are a fixed ratio equal to the Gearbox ratio (1:1 when the 'GB' is the crankshaft ). If you know one, you know the other. If you have a GB, the EIS can display either prop or engine RPM, whichever you prefer.

[Randy]

If an injector partially clogs, it can send one cylinder lean enough to cause problems. Watching EGT trends gives an indication of the health of the injectors as well as what th ECU is doing.

Leaving auto fuel in the fuel loop against the injectors for long periods has been known to plug up injectors.

Randy C
RV7A Sube STI non boosted
270 hrs

[TSwezey]

Originally Posted by DGlaeser

A tach pulse is typically taken from the ignition - either the ECU or magneto depending in the engine. Prop and engine RPM are a fixed ratio equal to the Gearbox ratio (1:1 when the 'GB' is the crankshaft ). If you know one, you know the other. If you have a GB, the EIS can display either prop or engine RPM, whichever you prefer.

This is not true for his setup. There is a clutch that is activated at about 1000 RPMs I believe. If the clutch is slipping for some reason he really wouldn't know the exact RPMs of the prop if he was running off the engine rpm sensor. On my plane I had a 1.72:1 reduction without a clutch so I knew my engine rpms from the prop RPMs.

I would install an O2 sensor and the automotive stores have a great gauge that hooks right up to it that displays you mixture. I used it all the time to fine tune my engine.