Monitoring CHT and EGT

[Elombard]

What about one of those trick stack type electronic gauges that lets you have virtually limitless readings. You could have 6 CHTsd and 6 EGTs plus more. They arent even that expensive anymore. You could mount it on a flip down hinge under the dash and have no 2" holes.

[Green 912]

If you have enough gauges you won’t even have see it when you rear end the car in front of you while looking at a reading or fiddeling with the swiches.

EGT and A/F mix are what you need to set up and monitor your motor. You can get an EGT probe that requires no welding you just drill a small hole in the ex pipe. Install the sensor within the first 6 inches of the ex port. BeepBeep is spot on CHT will tell you how the fan is doing but good EGT and A/F mix readings rarely also have high head temps on the average motor. Head temp and oil temp tend to go hand in hand anyway. (race or high peformance motors excluded) There is a good dual EGT gauge available, no fiddling with switches. You install one sensor on each side and while driving you can with only a glance see how both sides are doing and compare carb tuning and linkage setup as well.

[RoninLB]

Originally posted by 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!

IMHO , best to monitor CHT when tayloring engine load, as Superman discussed.. best to monitor EGT when dialing in induction system/tuning, especially carbs.. and 6 probe EGT will detect a problem quickly with fuel distributor in fuel injection or an indivudal carb[1 out of 6].. hopefully preventing a hot piston from wrecking the engine.. a damaged piston may/should be difficult to notice when driving.. by the time a burn piston is diagonised it's too late.. and to my understanding the pros install EGT 1 inch from cyl. head/down the tube.. don't know what kind of readings you would get at air injection hole, which is hardware store pipe thread brass plug, I believe. I hope it would be OK/don't know/it's not professional.. and a good A/F system is available for big big bucks. I think it's because of the delicate/expensive/short lived probe.. the routine A/F we see is mostly worthless... and CHT and oil temp don't always go hand in hand. try driving thru a desert before the sun comes up. the readings now look great. when the hot sun heats ambiant air to 110deg. your oil temp will rise and CHT will be close to no sun readings...............Ron

[ohecht]

OK...it looks like I will not be able to put in any EGT probes in the right position until I have a better reason to pull the motor or remove the SSIs. I do not see any plugged EGR ports on my heads.

I considered putting them on the exposed part of the SSI piping near the front of the car, which is probably the closest to the heads that is accessible. Would that location work?

I will probably put in a dual EGT/CHT gauge and just run those leads later.

My question for those monitoring CHT is, does it have any value? I think EGT is more direct, but have you found value in therms of monitoring engine health by monitoring CHT?

Thanks,

Olivier

[RoninLB]

Originally posted by ohecht
My question for those monitoring CHT is, does it have any value? I think EGT is more direct, but have you found value in therms of monitoring engine health by monitoring CHT?


Olivier

Well Oliver, if not for track use, then does CHT have any use on the street? I would say it's a personal opnion. what do you do on the street? in my situation I want a CHT, and watch it like a Hawk, sometimes.. The CHT feedback is immediate. oil temp feedback is after the fact. a good example of when it comes into play in my 911 in when coming into LA from the north on I-5.. everything OK at 70-80mph in 5th. outside it's 80deg.. traffic is routine 3pm stuff.. when I get to the hills north of the city, traffic moves between 60-75mph, variable.. but now my CHT starts to climb on this hill in 5th at 65mph..if I can get to 75mph I'm fine, but I can't. if I have to slow to 60mph in 5th I can watch the CHT climp very quickly. so, screw it.. I do 4th at 60-65mph and avoid the left lane, which is not really much faster. except for a very brief time.. the CHT comes down where it belongs.. and my 911 has a fender cooler.. my 911 oil temp is usually at 170-175deg. thru routine summer driving.. and will run to 180-190deg thru 112deg desert heat at 3.8k-4k in 5th. so it's a personal thing.. I would definately recommend it for hill country, especially in summer hills.. doing the Rocky Mts. w/a CHT is important, IMHO.. by the time your oil temp reacts it's a done deal.. PIA to bring oil temps. down. a CHT prevent high oil temps. and I mentioned on another thread that a CHT is an good indication of how hot outside temps cause your 911 to raise oil temps a bit. if good CHT, then rpms/mph are OK.. and a side benefit to routine street in winter is that watching the CHT at start up is a great indication of how the warm up is going.. if I drove a water cooled engine, it's a different game. so a CHT is not necessary for everyone.. but a volt meter is.. you got a voltage ga. right.................Ron

[RoninLB]

Originally posted by beepbeep
Dear Olivier:

EGT is very important parameter in my book.
Cheers!

it's also important in my book.. new SSI and Monty , when installed, will prove how important EGT is to me.. big bucks, big monitoring, big entertainment...........Ron

[ohecht]

I definitely have the volt gauge to put in...I had been using the pilot display on my Passport 8500, but they're illegal in VA. (8500s, not volt gauges)

I think I will wait until I have the proper access for the EGT, especially since the senders are ~$27 each!

In the meantime, I will monitor all 6 CHTs.

I am leaning towards a dual gauge and a 3-position switch that will show me front, middle, and rear cylinders as pairs.

My idea is to use this as a gauge of how the cylinders are doing compared to each other in terms of mixture, timing, cooling, spark, etc. I know there will be variation based on cylinder locations, but I should get used to the baseline readings fairly quickly. I am also going to put in a A/F gauge and probably a vacuum gauge in the engine compartment to facilitate tuning, etc.

I am definitely sensitive to the issue of information overload, and I do not plan to switch between cylinder readings when driving unless I am diagnosing a potential problem. I don't even look at my speedometer most of the time, especially now that the 930s wheel blocks it almost completely.

Olivier

[RoninLB]

Originally posted by ohecht
6 CHTs.

unless I am diagnosing a potential problem.
Olivier

OK.. different needs than me.. I want the 6 EGT to monitor a clogged fuel dizzy line, or a single carb [1of6] instantly, and a single or dual CHT to measure operating load.......Ron

[tbitz]

wouldn't it be a cool if a single CHT gauge would sense all six cylinders and automatically display the one with the highest temperature.

This circuit wouldn't be too complicated to build...

[RoninLB]

Originally posted by tbitz

This circuit wouldn't be too complicated to build...

I'm in motion for a complete exhaust system right now.. and my cars somehow become very personalized or neurotic. your convience.. could be good entertainment soon .........Ron

[beepbeep]

Gentleman:

Heat in cylinder heads is produced by combustion, the very same combustion that EGT-sensor measures, directly.

CHT is nothing but lazy way of measuring EGT that is also influenced by fan-RPM and much less "instant".

Oil-temp is even more delayed and fuzzy measure of CHT, this time influenced by EGT, CHT, fan-RPM, airflow trough front cooler etc.

Personally, i believe that EGT is the way of monitoring how engine feels and much, much more accurate and exact than monitoring CHT or even worse, oil-temp. I understand that CHT is cheaper, and doesn't involve drilling and welding-in EGT-probes, but you get what you pay for in this case.

P.S. On the other hand, you have N/A motor, and EGT isn't as important as in turbocharged engine, where things can happend very fast and destroy engine.

[RoninLB]

Originally posted by beepbeep
EGT-sensor measures, directly.

CHT is nothing but lazy way of measuring EGT that is also influenced by fan-RPM and much less "instant".


Personally, i believe that EGT is the way of monitoring how engine feels and much, much more accurate and exact than monitoring CHT or even worse, oil-temp. I understand that CHT is cheaper, and doesn't involve drilling and welding-in EGT-probes, but you get what you pay for in this case.

everyone is entitled to an opnion... Some guys swear by an EGT alone. but EGT cannot tell you when the engine is about to be damaged, it's the temperature of the engine metal itself that is imp., IMO. an EGT would be showing a safe engine temperature before damage. because the engine may be able to overcome increasing friction of the expanding piston in the cylinder or a burn piston/valve, etc. but when the power is reduced, and the engine can no longer overcome the increasing damage, the engine seizes, at worst. . a CHT would have been showing the increase in cylinder head temperature..and, an EGT cannot warn you of a broken cooling fan belt, or a lack of oil... so, IMHO, drive w/a CHT. and tune w/EGT and an expensive A/F gauge.. and I'm not an expert on this.. Sherwood Lee knows more about this stuff than me ...............Ron

[ohecht]

I am assuming that relative temperatures (to eachother and some baseline when the engine's condition is somewhat known) is the most important, since I don't know of specific spec for each engine under each condition.

I would be much more inclined to do both or to do EGT if I could mount the sensors on the exposed part of the SSIs. Would this give me readings I can use in a relative manner? Or would they be off the scale on the low side and useless?

The time pressure is because I will be running wires from the engine compartment to the dash area for other projects while I am cleaning and doing a lot of stuff in the interior. I just can't risk breaking an exhaust stud pulling the SSIs just for the EGT sensors.

I like the point regarding CHT that it would show cooling fan or air ducting issues as well. EGT is certainly a more direct measure of what is going on in the combustion chamber, but I think CHT is valuable too, as it would show how all the systems designed to cope with the current temperature are handling it. (i.e. 1700 F EGT on a cool night with plenty of airflow may be manageable without damage, but lower EGT temps sitting in traffic could be more of an issue) My uninformed opinion...

Olivier

[Don Delaney]

CHT and EGT are both good to have. Each has its advantage and disadvantage. The nice part about having both is being able to recognize detonation. When an engine begins to detonate the CHT will increase and the EGT will drop. With such a set up you will be able to detect detonation long before you can hear it !

[tbitz]

What kind of sensor are you guys using for CHT. Are the ones that go under the spark plug available (where?). Are they thermocouple or thermister based?

[TimT]

When an engine begins to detonate the CHT will increase and the EGT will drop.

BINGO!!!!!!

Ive heard that before.

Porsche engines are much to noisy to hear detonation unless it is already doing damage.

[ohecht]

Tony,

Aircraft Spruce and Wicks (aircraft supply) have good prices on 14mm CHT senders that go under the spark plugs.

The gauges they both carry are also high quality and reasonably priced. I have been looking at all the Westach products they carry.

Westach has a site at frostalarm.com, and they are helpful over the phone, but they were quick to direct me to the retailers and told me I would save close to 40% by not buying direct from them.

The cool thing about Westach is that they will put together a dual (or triple or quad) gauge for you using existing "faces" they already have for no extra cost compared to a "standard" gauge with the same number of readings. They will also make custom faces, but that costs extra (like $50) and takes a little while.

I was going through all kinds of combinations and I am still not sure what the best way to combine reading is. I may have air/fuel and trans temp as single gauges, and then a dual CHT/EGT gauge with a 6-position switch to display any one cylinder at a time. I would hook up the EGT later when I have better access and leave the gauge on the hottest cylinder (#3) while driving, but still be able to switch during tuning, health checks, or diagnosis.

Olivier

[RoninLB]

Originally posted by ohecht
Tony,

Aircraft Spruce and Wicks

I was going through all kinds of combinations and I am still not sure what the best way to combine reading is.

I may have air/fuel and trans temp as single gauges, and then a dual CHT/EGT gauge with a 6-position switch to display any one cylinder at a time.

Oliver..the Aircraft Spruce catalog is full of info.. get it before spending $$.
..."combination"..haven't done full CHT & EGT install yet, but my concern is more engine damage than max HP tuning. like if a fuel dizzy or single carb gets fuel starved. I think 6 EGT probes w/constant monitoring is the way to go for tuning.. monitoring CHT for engine load is 1 probe, IMO.. but not individual cylinder load. and if "pinging", then all cylinders would be affected
... and when Don & Tim wrote "When an engine begins to detonate the CHT will increase and the EGT will drop" that confused me.. I figured that if a lean condition caused pinging that EGT would increase.. so, I guess that it's the total volume of EGT heat that decreases and indivudal cylinder load increases.........Ron

[jyl]

Oliver, have you made any progress on this project?

I am interested in a CHT gauge too, unsure about an EGT gauge, and interested to know what you found to be the pros and cons of X-way gauge with Y-way switch - e.g. dual CHT/EGT gauge with 6 way switch, etc.

[ohecht]

A lot of my projects have been delayed, but I was actually thinking about this again this morning. I will probably put in the wiring while I am cleaning underneath the carpeting, etc., but my main concern is breaking an exhaust stud just to remove the SSIs to put in the EGT probes. It may not be worth the risk until I have a better reason to remove them.

I am also looking for a good way to mount the gauges that looks somewhat professional. The 3-gauge pod that Performance sells and describes as matching the 911 interior grain is just a piece of rubber that doesn't even seem to have the right angle for the dash.

I am going to re-list my parts requirements today and think it through again.