Hallo,

i think there are many myths around the best EGT Temperature. So i thought writing down what i know about EGT's and their relations and throw it into a discusstion.

i don't know if everything is correct, so if something is wrong, feel free to correct me.

First of all i think we must talk about the same, so the position of the EGT probe is important. I think most ppl
overcome that 1-2" after the manifold flange would be the best.
And especialy for our hondas the 3rd cylinder because its normaly the hottest.

So what change EGT? AFR, Ignition Timing and Type of Fuel (fleme front speed)

What do changes in AFR?
- EGT's are highest at around 14.7:1 AFR
- when the mixture is richer then 14.7:1, the EGT will drop
- and if the mixture is leaner then 14.7:1, EGT's will also drop.

As far as i know, there is no rising in EGT temp if the mixture is far too lean OR far too rich (Question to the pro's: is this correct?)

what do changes in Ignition Timing?
- Retarding ignition will rise EGT temps (Question to the pro's: does the temp drop if ignition it far too retarded?)
- Advancing ignition will lower EGT temps until the temps flat our. This will be the point where your timing is near optimal (i guess). If the ignition is advanced above this point, EGTs will drop because of detonations.
(Question to the pro's: is this correct?)

what does flame front speed do?

- lower octane fuel is burning faster => EGTs will drop
- higher octane fuel is burning slower => EGTs will rise
- leaner mixtures are burning slower => EGTs will rise
- richer mixtures are burning faster (until a certain point) => EGTs will drop.

what do compression ratio do?
- higher CR => lower EGTs (don't know why!)
- lower CR => higher EGTs (don't know why!)


if someone has to add or correct something... feel free to discuss...
please don't blame me if something is wrong, it was only a short writedown and this should be a discussion.

If you post something, please look that you can explain what you write... do things like "i have heard from a friend, blabla"

Best regards
Malte.

 

Only 1/3 of engines produced heat is used to power the engine. the other third is absorbed into the cooling system and the other third goes out the exhaust. With that in mind, it will answer some of your questions.

"Retarding ignition will rise EGT temps (Question to the pro's: does the temp drop if ignition it far too retarded?) "
-The temp will not drop because more heat will be exiting the exhaust instead of powering the engine. The more you pull, the higher the EGT.

"what do compression ratio do?
- higher CR => lower EGTs (don't know why!)
- lower CR => higher EGTs (don't know why!)"
There are some other factors but with higher compression, more heat will be used to power the engine and less will go out the exhaust.