cht or egt

[Yves]

I'm contemplating on going towards sequential injection in the future. This would entail a way to measure the temp of the combustion in each cylinder. Now would CHT work as well as EGT ?

[billr]

I doubt CHT is going to do much good for you on that. Even if you have iron cylinder heads, conduction through them and heat transfer from the coolant are going to stabilize the whole head to nearly one temperature. That's usually a prime goal of the head and cooling system design, to avoid "hot spots" in any areas of the head.

[elutionsdesign]

Billr is speaking cleanly, EGT will be a much faster response than CHT, for something actually happening.

[billr]

I meant to also mention that it is usually a lot easier to add ports for individual cylinder temp sensors to the exhaust manifold/header than the cylinder head.

[Yves]

I meant to also mention that it is usually a lot easier to add ports for individual cylinder temp sensors to the exhaust manifold/header than the cylinder head.

Bill,

A cht is under the spark plug in place of the regular gasket. So it takes the temp from the spark plug which is in connection with the combustion temps. It's used all of the time in aviation.

Interesting read here :

http://www.jpitech.com/press_releases/Bush_Article.pdf

[racingmini_mtl]

Do you have an air-cooled engine or a water-cooled engine? I'm not aware of CHT being used for water-cooled engines. Those aviation engines where CHT is used are air-cooled.

In any case, you wouldn't use CHT for tuning. EGT will give you an immediate information on combustion temp.

Jean

[billr]

I forgot about those spark-plug-washer temp sensors, thanks for the reminder. However, a T/C in the exhaust gas stream is still going to be a lot faster and more accurate. The tip of the plug may be a good indication of transient combustion temp (that's why "plug reading" is so revered), but the base where it contacts the head is a much more stable temp. That's the primary principle of controlling plug heat ranges, tip temp is determined by how much heat is allowed to conduct back to heat-sinking that the threads/washer-face provide.

[Yves]

I was viewing this from a more practical point of view. To install egt's would involve taking the headers of which on my car is very lengthy/difficult job. The mounting of cht's would be a breeze compared.
I don't think the area around the spark plugs is cooled.

Only on air cooled engines ?

[kaeman]

EGT will be more reliable info for the computer to use, the response time is much quicker and will provide valuable information to the ecu quicker in case of a problem, by the time you have a temp change in the CHT on your plugs, the exhaust smoke out the mufflers will let you know about the burned pistons.