Max EGT? Options

[technicalninja]

The title is the question.

I know what to look for with water-cooled stuff.

I have no experience with air-cooled stuff yet...

What say you?

Is there a normal range?

A never exceed number?

Anyone ever use 4 thermocouples?

Was there any noticeable difference (#3 is of concern to me)?


Thoughts, tips, any data would be greatly appreciated!

[gereed75]

I also come from an aviation background. What Greg said

EGT is a different way to “monitor” mixture. Pretty much what was available prior to having O2/AFR equipment readily available.

If you monitor AFR via O2 sensor then I would say also reading EGT is maybe superfluous but nice to know.

I agree with Greg, max is somewhere around 1450 F., depending on a number of variables. Max power is produced somewhere around 100 - 75 rich of peak, corresponding to AFR around 12.5 -13. Best economy (and lowest CHT) is 25 - 50 lean of peak, AFR around 14.

Your car’s computer is trying to operate the engine in these ranges depending on throttle position RPM, load, MAP , engine temp, IAT etc etc. the computer adapts fuel flow and timing to produce what it thinks the situation calls for.

One other note, the EGT that the probe sees is highly dependent on where it is placed in the header. The temp inside the “flame cone” (my term) varies considerably by location within a band of an inch or so.

On another note, I know of no modern engine control system that monitors EGT as a control parameter except maybe in turbo applications. Then it is call Turbine outlet temp.

[stownsen914]

Decades ago, we didn't have reasonably priced wide band O2 sensors, so people did use EGTs to tune racecars. I still have one on my 914/6 racecar, mostly as a vestige as this point. As suggested, AFR is probably a better method as O2 sensors are more responsive than the thermocouples that EGTs use.

If you prefer an EGT, and assuming you put the thermocouple about 1.5-2" from the exhaust port as recommended, I was told by a couple Porsche racers that normally aspirated, aircooled Porsche motors like about 1200 degrees F.