Monitoring CHT and EGT

[ohecht]

While I am doing some wiring work, I would like to put in a cylinder head temperature gauge.

I am now also considering an Exhaust Gas Temperature gauge, and I am wondering if there is a significant difference between these in terms of engine condition.

I will also be running a mixture gauge, and I would like to know what sort of conditions would be noticeable only by having both CHT and EGT displayed. Or are they completely redundant on an automotive engine?

I wil probably use aircraft-style gauges and switches to monitor all cylinders and both sides of the dual (SSI) exhaust (selectively, though)

I know this is probably all "overkill" and I would be hard-pressed to even know how to react to abnormal readings, but this is just one of those "while I'm in there" projects and I think it will help monitor the consistency of an engine I plan to keep in one form or another for many years and miles to come.

Another question if the EGT is good to monitor: the gauge is 700 - 1700 F; is the only part of the exhaust that gets that hot closest to the heads? I ask because the probes are clamp-style that go through 1/4" holes, and I would probably not mess with anything too far upstream from the O2 sensor area.

Hopefully, I will have some good pictures, part numbers, and impressions once this is all done.

Thanks in advance,

Olivier
82 SC

[Superman]

RoninLB has a cool dual CHT gauge which he watches like a hawk. He reports that you can watch CHT rise while accelerating up a hill in a low gear. Change gears to move more air past the engine, and CHT falls again. I'd like one.

[ohecht]

Westach has some great gauges. It is addicting once you see everything you can monitor, and keeping it reasonable and deciding which to combine is the hardest part.

They can move around the scales on the gauge bodies, so you can customize pretty easily and even have custom scales made if necessary.

I am trying to stay with 3 2" holes and one will already have a voltmeter, so I am debating the last 2. I think EGT is overkill and that I would have to mess with putting a probe very close to the heads on the exhaust side, which doesn't seem worth it.

I am considering either:

A) single A/F gauge and combo CHT/trans oil (with 2 or 6 position switch on the CHT)

B) Dual CHT gauge (with either 3-position switch or just monitoring hottest cylinder on each side) and combo A/F & trans oil gauge.

I am still struggling with what to do with the information...I like the idea of being able to check each cylinder's temperature for airflow or fuel delivery issues, though...

Olivier

[beepbeep]

Dear Olivier:

EGT is very important parameter in my book. CHT is nothing more but a laggy function of EGT that is also influenced somewhat by fan-speed (reciprocal).

If you have to choose between two, go for EGT. It will accurately tell you your A/F condition, even when lambda sensor is overheated and delivering false values.

If possible, install EGT-sensor as close to cylinder as possible, prefferably one per cylinder directly under cylinder heads (use 6-position switch to select each one).

Cheers!

[ohecht]

What sort of sending units would you suggest?

I have never looked that closely at the space around the exhaust sides of the heads...I have what I think are SSIs or back-dated exhausts (into a dual inlet muffler, and provisions for heat)

I'd like to avoid welding in that area if possible. Here is a link to the options for the sending units:

EGT sending units

Thanks,

Olivier

[ohecht]

BTT

[tbitz]

I wonder if you can stick the EGT sensors in the EGR injectors locations. My smog pump is gone and the EGR injectors are plugged. They are right at the exhaust outlet of each cylinder.

[TimT]

Y0u probably could use the EGR ports, however they have an odd thread pitch if I remember, im not sure if any mfg. makes EGT probes with the dia and thread pitch

[tbitz]

Could remove the injector, drill it, and weld/braze K-type thermocouple in there.

[Zeke]

In kart racing, we used EGT 3" from the port screwed into a bung welded in the head pipe. The probe was inserted so that the tip was right in the center of the pipe. Readings were virtually real-time, whereas the EHT simply let you know the overall conditions with regard to engine temp. With no water temp, this, with oil temp, is all you have for overall readings. It has been said that if you take care of the fuel/air mixture and get good exhaust temp readings, that the rest will take of itself. I don't buy that. On the kart I had both (2-cycle, no oil temp). On my race car I will have all three.

[ohecht]

Did all SCs have EGR ports? I don't think my car ever had a smog pump.

Tony, is the injector you are referring to the air injector from the smog system?

I have to look at my exhaust again to see how accessible that part of the exhaust system is. It is tempting to have a gauge checking the temp and mixture/burn performance of each cylinder.

I think it would be great to track down ignition misses and dirty injectors.

Olivier

[tbitz]

I don't know if all SC have them.

I'll try and get under the car and take a picture.

[efhughes3]

Wow, for a minute seeing the talk about EGT and CHT made me think I was on my aircraft BBS!

[beepbeep]

Best EGT-sensor position is probably in air-injector holes. It's as close as it gets.

Even better, holes are allready there!

[ohecht]

Are these holes in the heads or exhaust?

Pictures would be great, as would thread size and the right sensor depth.

I have SSIs, which I would doubt would have air injector holes.

Olivier

[ChrisBennet]

I think the air injection ports are 10x1.0.
-Chris

[RoninLB]

from what I have read.. the best place for a EGT probe is 1 inch from the head/down the tube.. this is where I will do it........Ron

[tbitz]

Here are pics of the smog air injectors just beside the exhaust manifold.

Sorry about the poor quality in the pics. A better camera is on my X-mass list.

[ohecht]

Is what I see in the picture just a plug for the fitting that is not used without smog equipment?

[tbitz]

It part of the original smog gear. The metal line that came from the smog pump has been cut just before the injector and the pipe has been brazed to seal it.