I am contemplating pre/post turbo pyro trade-offs. The only really compelling reason (for me) to go post is the often repeated warning that a broken pyro pre turbo could toast your turbo.

Does this ever REALLY happen? Or is it like the cat in the microwave story. Everyone has heard it, but no one can produce a name and an address.

 

It may happen, but I have never heard of a thermocouple failing. I always install thermocouples pre turbo and have been assured by ISSPRO that their thermocouples can withstand temperatures much higher than what we subject them to. The benefits are much quicker response to changes in EGT and you know exactly what the cylinder EGTs are. You must take a guess at cylinder EGT when you place the thermocouple post turbo.<br>Marc

 

I have ran mine post for 2 years now and I'm moving in pre on Tuesday, tired of having to add and guess at the real temp. Have never heard of a probe going out, I think if you get it that hot you will have bigger worries. ???

 

I'm not sure why one would break. It's stainless steel and they are tough. The probe internals will fail before the tip breaks off in my opinion. Those things are tough.

 

I have been running a pre-turbo thermocouple since 6k miles on my truck (now has 83k), I check it about once a year, it doesnt seem to be degrading.<br>RM

 

Cummins specs the ISB engine at 950 degrees post turbo. So basically if you stay stock, you need to be post turbo. This figure is good to about 28 lbs boost (the ETH wastegates at 26 I believe). The real issue is protecting the pistons from high temperatures -- cummins performed a large body of work to correlate piston temperatures with post-turbo EGT measurements. why did they do this? to save turbos from disintigrating thermocouples.<br><br>fast forward to relevant conditions today: <br><br>1. If you're running stock you don't need a pyro anyway. If you're bombed at all, then you are running outside of the Cummins operating conditions appropriate for the post-turbo spec, and you need to run pre-turbo. 1250 degrees is the max pre-turbo EGT.<br><br>2. Thermocouple breakage isn't an issue today. It has been in the past, and keep in mind that cummins' work reflects commercial duty trucks with 500K to 1 Million miles on them. <br><br>The only argument for a post-turbo thermocouple is to more accurately determine a safe shutdown temperature. But the accuracy you gain here is more than overshadowed by the loss in accuracy in accurately determining a safe running temperature. The 300 degree pre-to-post temperature differential is only good for stock turbos and boost pressures of 28 lbs and lower. Folks with upgraded turbos, or just running higher boost pressures, will experience a greater (than 300 degree) temperature difference pre-versus post, so Marc is right in that the post-turbo measurement is more of a guess than you want to make. Bottom line is this: protect your pistons, mount your thermocopule pre-turbo, and always run below 1250 degrees. The broken thermocouple problem isn't an issue today.