Afr’s vs exhaust temps

What is the safest and better way to tune a diesel. Afr’s or exhaust temp. What would be the max afr or temp you would want to see.

For me this will be EGT and this is why:

You can have a ton of Air Mass per stroke but if your running small injectors and extend the injection duration way to far you still get smoke and hi EGT as your end of combustion still maintains in the exhaust stroke and you lambda or o2 probe will show happy numbers on oxygen left.

Also exhaust pressure or EMP play a big part getting Hi EGT numbers as well. 5bar EMP while not running a wastegate easy makes 200C more EGT in front of the turbine.

What EGT is save? Cannot tell this for all. We try to run 800C max due to the turbine housing starting to deform from that point onwards and aging will go a lot faster as well.

Silly thing is some bigger turbo have there max efficiency @ 900C EGT so in order to get longer live time out of our exhaust manifold/turbine housing we start building with material that can withstand 1000C and we going to use the TiAl V band turbine housing as well.

One thing I did not mention. On a petrol engine there is not a lot of oxygen left in the exhaust gas stream. A diesel on hi RPM has lost of oxygen left so hi EGT and oxidation as there is oxygen will degrade exhaust system a lot faster as metal simply burn away and it even looks like charcoal overstepping the limits.