I've been experimenting with idle tuning and noticed something I didn't expect.
When testing exhaust manifold temps with a pyrometer I recorded 680degF @ the #4-#6 ports and 450degF @ the #2 port when my BLM/INT was @ 128.

I added fuel to idle VE table and now have a 118.5 BLM and the pyrometer reads 450degF #4-#6 ports and 300degF @#2port.
I thought that the rich condition would cause the EMT to increase?
I tried running lean(BLM132) and the EMT went higher (#4-#6 780degF & #2port 520degF)
Since melted plug boots(#3-#5 & #4-#6) started this quest...and a wise man
stated "Don't tune to the numbers give the engine what it wants"...
Should Keep it "rich" or something in between?
Comments?
Other's experiences?
GEN1 383sbc LPE74216 cam First TPI intake (pre smog iron heads iron corvette 2.5in exhaust manifolds, no cat.

 

more fuel and more timing(before knock anyways) will GENERALLY give you lower EGTs, but that's not always a rule.

 

Check out this thread...
https://www.thirdgen.org/forums/diy-...cle-above.html

The initial link doesn't work anymore but there is one at the bottom that still worked today.
There is some good info on how exhaust temps change with mixture and timing. Good read if you haven't seen it yet.
Jp

 

Wow that's some good info! I just need to digest and find a EGT and CHT gauge to go with my WB02! Thanks!

 

As Grumpy (RIP) stated, The CHT is the same as the Coolant Temp in a water cooled application so you're good there.
The article is good at showing the relationships, I've read it several times and still go back for reference at times. We don't have control over the Manifold Pressure (MP) like in the article but the theory of operation relates the same.
The main thing I saw from it was how EGT is max at "just below" peak HP then drops on either side.
Mainly when tuning we are going for max power and that puts us over the curve on the EGT. When you lean it out the EGT goes higher...
But if you were fueling on (or before) the peak of EGT to begin with the temp would actually go down when leaning it out for better economy. Neat obsevation.

 

Is this assuming no change in SA? I could see where one might experience knock at peak
EGT, but then with the same SA tune for max performance a lean(er)
economy tune should be achievable. Anybody try this with anything other than an air cooled airplane engine? The pyrometer is not as accurate as a EGT thermocouple, so I think this would best be done with the most accurate measuring device.

 

That is correct, No change in SA for his tests.
That's what was nice in that it showed how fuel only effected the outcome.