Read my post under "24V engine discussions" listed under Pyro install. The reason for the large tempature drop after the turbo is the exhaust side turbine housing absorbs alot of the heat and dissipates it to the engine compartment. The faster you are driving means more air will be forced into the engine compartment and aid in cooling the Turbo. Also, ambient tempature outside will affect this reading also. Thats why simply adding a few hundred degrees to the POST turbo reading is not accurate. Where Cummins and Cat mount there Thermocouple on there larger over the road trucks is totally irrelevant. We are driving pickup trucks, people seem to forget that. Over the road trucks and bulldozers dont have performance boost computers, Fuel controlls, and the stuff we put on. These things make the ISB do things it was never intended to do. That is why it is so important to monitor EGT's and Boost pressure.
Almost everyone on the TDR modifies there trucks for more power (Injectors, Exhaust, Induction, Power edge boxes, bigger turbos, etc). What this obviously says is that we feel Cummins engines need more power. In other words, We want to "Improve" the ISB, better fuel economy and more power. This proves a good point, why do people say that "Cummins mounts there Thermocouples Post Turbo on thier engines so i will too since they obviously know what they are doing", well if you believe in Cummins so much and think they know whats BEST for your engine, WHY ARE YOU MODIFYING IT IN THE FIRST PLACE!!, Obviously it's NOT how you want it. If it was, and you believed 100% that Cummins does everything right,you would not even touch your engine. your saying Cummins SHOULD have used bigger injectors, Cummins SHOULD have a bigger turbo, Cummins SHOULD have an adjustable fuel computer. , but they did'nt, so i will add one myself. BUT, something as simple as Thermocouple placement, you think "CUMMINS KNOWS BEST!", do you get my point.
Banks, Jannetty, TST, and others all say mount the Thermocouple pre Turbo, and alot of you say, "Thats wrong" but at the same time, you buy thier exhausts, injectors, computers, etc. I just dont understand the logic.
I think alot has to do with it is easier to mount the Thermocouple Post Turbo. Also, people are paranoid that the Thermocouple will catstrophically fail. As i mentioned in my other posting, The chances of that happening are so remote (Virtually Non-exsistant). I have never heard of it happening without an engine failure causing it. I have been asking all my Diesel Mechanics where i work, Nobody has ever heard of one failing, EVER. its just not going to happen. I can honestly say The only way that could break is if it was hit by something flying through your exhaust, like a valve fragment and if that happened, your turbo would be destroyed anyhow, along with your engine. The other thing is people are nervous about drilling and tapping there exhaust manifolds. Its really not that hard, and it is worth it in the end because you WILL be getting the most accurate exhaust readings possible. And the issue with metal chips falling in the manifold and going through the turbo and damaging it, using the vasaline and magnet deal will eliminate most of them and the few that remain are no big deal. I have installed Thermocouples on 3 Rams and well over a dozen other turbo Vehicles (Grand nationals, A twin turbo mustang, And several different pieces of heavy equipment). I never removed a turbo to do it. What little fell in will blow out the exhaust harmlessly. Just start the vehicle and within a few seconds at idle, it will all blow out. The RPM's are too low to cause any damage, the WORST a piece of metal could do at idle is jam the impeller. All you do is shutdown, remove the intake hose and turn the turbine backwards to dislodge it, you wont bend anything at such a low speed. If you are STILL nervous, take the 30 minutes or less to remove the turbo. No big deal. Well worth the simple, accurate EGT readings that in the long run, will save your turbo.
Attention: TDR Forum Junkies 
