this is a copy and paste from a rant on went on about 2 years ago
When I have a engine on my dyno, I DO NOT use EGT’s to tune a engine. I use BSFC and O2 sensors (with ALL fuels) but even with that, I pull the plugs ever time I make a timing change. I use EGT probes to tell fuel distribution and other things, I never use or heavily rely on EGT as A/F Ratio determination
Using the EGT probes for fuel distribution studies is their greatest value.
You can't ask some other racer what EGT is best for you .
example= no matter how well you tune a 9:1 normally
aspirated engine, its EGT's will be higher than a similar
properly tuned engine with 15:1 Compression Ratio .
....no matter what you do , the 9:1 CR engine is going to have
higher EGTs because it will waste heat out exhaust more than
a 15:1 engine, or any CR higher than the 9:1 CR reference point .
If you asked a group of racers that all had their engines
perfectly tuned and maxed out with the best possible ignition
timing curve and A/F Ratio ....
one racer might say 1350 deg F ,
another might say 1250 deg F ,
another might say 1150 deg F,
another might say 1050 deg F
.....they could all be correct and have the very same A/F Ratios
.....the varying EGTs depending primarily upon Compression Ratio,
Volumetric Efficiency percent % , Combustion Chamber/Piston
top design and camshaft design.
Another thing you have to watch out for is
where are you placing the EGT probe??
1-at 12 o'clock or so ...
2-How far away from heads exh port flange ???
3-How deep is the EGT probe protruding into header pipe diameter ????
4-EGT probe type and response time
all these factors greatly influence EGT temps making
it very much impossible to directly compare EGTs between racers
if no standards are set to probe placement
So basically , if you walk around the pits at a National Event
and ask the SS racers that have CR from 9 to 11:1 mostly ,
they'll tell you 1250 to 1350 EGT and maybe a few at 1450
you ask the ProStock and Comp guys with 16+:1 CR
they'll tell you 1000 to 1150 deg F
maybe some of the very large Mountain type engines
with HiCr tell you 850 to 1000 deg F EGTs
Hi Compression Ratio = Lower EGT temps
Lo Compression Ratio = Higher EGT temps
Correct ignition advance(32+ to 40+ ign deg range)= Lower EGT temps
Wrong ignition advance ( below >25 or so deg range)= High EGT temps
..... burn slower and later in stroke , continuing to burn
while exhausting and if severe...cycling/snowballing into rising
coolant temperatures, preignition, then detonation.
bottom line is you need to tune your car by reading plugs and adjusting from there.
https://board.moparts.org/ubbthreads/ubbt...tml#Post2020087 Joe
