Here is the text of the private message I received via the TDR website several years ago. I have deleted the engineer's name to protect his identify. I had pm'd him inquiring about the maximum allowable sustained exhaust gas temperature the HPCR engines could tolerate.
"Harvey,
Happy holidays! EGT's are always a touchy subject due to differences in measurement locations and differences in the devices used. It's difficult to say what a true upper limit is on EGT for the ISB engine because we don't test it above the "stock" settings. However, I can tell you what we have measured on the latest 2004. 5 and 2005 engine configurations.
MY04. 5/ 325 exhaust temps can be as high as:
Sea Level: 1375 Deg F pre turbo, 1125 Deg F after turbo.
Altitude: 1450 Deg F Pre turbo, 1200 Deg F After turbo.
The above are typical temperatures from development trips. The MY04. 5 product was developed to operate at these temperatures. I have no idea what would happen at temps above these, because they haven't been tested.
I don't mind you sharing these numbers as long as the source remains anonymous. We don't want someone thinking "Cummins approves this temp on my engine because . . . " . This really isn't a guideline or approval or anything, just some results from tests we've conducted on stock engines.
I hope this help answer you question. If you need anything else, let me know!"