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CHT vs CTS 
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QFP80 - Contributor
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Joined: Sat Sep 24, 2011 12:27 pm
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Just to be clear I am talking about, Cylinder Head Temp sensor (CHT) and Coolant Temp Sensor (CTS).

The only implementations of CHT sensors that I have seen are K type washers that mount under the spark plug. Is this correct?
Some times CHT seems to be used to describe a coolant sensors by mistake.

For EMS related calculations would the CHT be the best measurement to use? Coolant temp would not be the same as the temp of the cylinder.

CTS would be essential for electric fan and electric water pumps. I assume the costs of having a CHT and CTS does not justify the benefits hence its not used.

So my question is, would there be much of a performance difference between these two measurements?


Mon Dec 19, 2011 6:14 am
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Perhaps we need a new acronym? FreeEMS has one variable and it is "Engine Temperature". I call it Coolant/Head Temperature, abbreviated to CHT. CLT is commonly used for coolant temperature, however the FreeEMS code is designed from the start to support air cooled engines where head temperature (a larger number) is used. CLT is misleading, however I guess, if you're posting on this, CHT is too. Perhaps EET Effective Engine Temperature? MET Measured ET? OET Observed ET? AET, Apparent ET? The only code currently driven by this number is the ETE table, Engine Temperature Enrichment.

Head temperature is solely used for air cooled stuff, coolant temp is the right choice for anything water cooled. Oil isn't as useful as it lags reality by a lot and therefore leads to a difficult to get right warm up tune.

I hope that helps! Thoughts?

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Mon Dec 19, 2011 9:52 am
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QFP80 - Contributor
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Joined: Sat Sep 24, 2011 12:27 pm
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Well the reason for the post is that I am thinking of using a CHT sensor instead of mounting a second CTS (CLT), hence started to research the difference.

As I am yet to experience what its like to tune an engine, how sensitive is the ETE table?


Tue Dec 20, 2011 3:31 am
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Install a coolant temperature sensor, in the head, before the tstat, and be happy :-)

Anything that goes around a spark plug feels strongly like a temporary solution and not for long term permanent use.

Warm up stuff isn't super sensitive, however it is very important. You get literally twice as much fuel demand cold as you do hot, and that's just in NZ, in Canada it could be MUCH more :-) The curve in the code base is what I tuned for my truck and it worked pretty well.

Fred.

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Tue Dec 20, 2011 11:50 am
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QFP80 - Contributor
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Ok.
So once the engine is warm it does not really matter much?


Thu Dec 22, 2011 10:36 am
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Right, if it has warmed up, and your tstat is functioning properly, it's a non issue. If you wanted to be old fashioned, you could connect your choke knob/lever to a pot and attach that to the temp input and set a PWM on an idle valve to rise with the pot and the mixture to change, and you'd have pretty much what a choke provided ;-) I don't recommend that, though, then you have no way of logging what is happening, no way of retarding the timing if it gets hot, etc.

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DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Thu Dec 22, 2011 12:08 pm
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