Just read this post from Robert at FP on facebook and it reminded me of this old thread.
Not sure if it's useful to anyone, but the old man knows his shit so I figured I'd post it just because.
Quote:
Back in the "DAY" (the 90's) we all had Greddy EGT guages and we never let them go above 850C for even a instant for fear of our engines melting away like the Wicked Witch of the West with a bucket of water on her. Today most people don't think they even need a EGT gauge since they have widebands, and that has a lot of implications.
First of all, the whole time we thought we were "tuning" with our EGT gauges, we were actually just making sure our parts didnt melt. Today we are all much more sophisticated and do our tuning with our widebands, many of us not even bothering to fit EGT gauges or even measure EGT at all. This makes perfect sense from the tuning perspective, because after all, you can't tune a ECU very well off EGT anyway.
What we overlook when we make this decision is that the typical "safe rich" tune supplies more fuel than can be burned during the power stroke and the typical "safe timing" is really retarded timing which puts even more of the combustion occurring during the exh stroke instead of the power stroke. Well you may already get where I am going with this... If there is a bunch of "safe rich fuel" left over for the exh stroke and the timing event was 4 degees later than it should have been then what you got there inst safe at all, you are doing the jet engine blowtorch routine inside the manifold, and your EGT which you are not measuring is getting absurdly high, easily reaching or exceeding 1000C without much trouble.
Inconel turbine wheels can tolerate operating at about 800-850C without being damaged, but flashing up above that for any real length of time will affect the material and make it weaker. each time it happens the material gets more and more weakened until the point where the tips just start to melt off. This imbalances the turbocharger and starts to put a lot of abnormal loading on the bearings which accelerates wear... all of this terminates when the turbine blades and or the turbine side bearing simply yield and break apart.
Couple things to take away from this note:
1) your EGT is important and you should know that your tuneup does result in a safe EGT.
2) turbochargers, particularly ones that cost less than $10-$15 thousand dollars, cannot deal with constant EGT above 850C.
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