Does anyone have EGT thermocouples both before and after the turbo that can give a direct comparison of temperatures before and after the turbo?

I know this has been discussed in the past but I couldn't find any actual comparison done by someone with dual readings.

The previous owner of my truck had already drilled and tapped for a TC after the turbo so that's where I installed mine. I am hoping to find a reference, or rule-of-thumb, so that I can get an idea of what the pre-turbo temperatures are based on my post-turbo readings.

BTW, my truck is an '06 and has no muffler...other than that it's stock.

 

I have both pre, & post turbo pyros.
As a rule of thimb, the temp pre turbo will be about 300*-400* higher than post turbo. So if you're seeing 1000* post turbo, pre turbo will be about 1400*.
Light loads will be about 100*-200* higher.

 

Wow really?! I didn't think there would be that much of a difference.

What is the difference at idle:Thanks for the response!

 

You'll never find a good conversion factor that works for all scenarios.

When your in-cylinder EGTs are high, the post-turbo reading will always be slowing to respond as you'll have some cooling due to heat absorption by the manifold and turbo. Once everything is heated up, you'll see higher readings longer on the post-turbo thermocouple since heat will be bleeding off the turbo keeping temps higher.

There are too many variables to accurately determine pre-turbo EGT from post-turbo EGT. The only way to accurately know what your in-cylinder temps are is to measure them as close to the cylinder as possible.

 

I know that there won't be an "equation" per say, to convert the post-turbo temperatures, but I'm just looking to get an idea for the differences in various scenarios so that I don't blindly follow the post-turbo numbers.

 

Here's how I do it.

When the truck is new and running good------- Look at the EGT numbers and get an idea where they should be.

If something changes, you should pay attention.

Easy as can be. There's no way you can get the same thing any other guy is getting, so yours will be different no matter what any of ours is. You don't need to worry about that anyway. You just want to watch for changes.

 

After just starting the engine the temps will be roughly the same.(idle speed)
After pulling a grade they will also be roughly similar to what i said before. As EGT rises/cools pre turbo, so does post turbo.
The only consistent thing I see after a grade, or heavy load is the post turbo temps will stay elevated longer due to the heat from the turbo, & manifold have to go past the post turbo pyro on thier way out the exhaust. My SS exh. turbo increases this too.

 

I'm not trying to figure out what range the temperature should be within...that's not my question. I'm simply wondering what the temperature drop is across the turbo under various circumstances. I know that my EGT's will not be the same as the next person's, but the temperature drop across the turbo should be similar, given similar conditions. I want to know this so that I can avoid temperatures that are too high, not so that I can see when there is a change in engine performance - which can be determined from a "change" as you mentioned.

 

So at startup they are similar, but after towing (or similar) and then idling down, the post-turbo temp will be higher for a while? Do I have that right?

 

The issue is that there are so many conditions to consider that will have varied ranges. If you go WOT, you'll see a spike in temperatures in the cylinder and manifold, but your post-turbo temps will stay lower since the turbo will be absorbing heat. So the difference in pre and post turbo temps will be large. The longer you continue to fuel at those levels, you'll see the post-turbo temp rise and close the gap between pre and post. When you reduce your fueling, your temps will fall, but the rate at which post-turbo temp falls will be dependent on how much heat was absorbed by the turbo and is now being transferred back into the exhaust gases.

So you'll have to figure in how hard you're fueling, how long you've been fueling that way and guesstimate how much heat your turbo is currently holding to determine the difference. That's a lot of calculation that has to take place to formulate a guess at what the actual pre-turbo EGT is.

Post-turbo works great for saving your turbo since you can accurately gauge safe shutdown temps, but for knowing what's really going on when you mash the pedal, the post-turbo will always be a less than scientific guess.

 

It varies too much for an accurate reading. That difference will be totally dependent on your setup, driving habits, and specific conditions at the time. Anybody elses numbers mean nothing, only what you see will matter.

Better off just drilling the manifold pre-turbo and be done with it.

 

Thanks for the description! I never thought about a lot of those points.

Again, I know that I'm not going to be able to find a formula or pin-point the temperatures, just some ballpark numbers so that I can always have that in the back of my mind.

 

The last page in this document, http://www.genosgarage.com/installat...lTips03-05.pdf

And this from the other site, http://www.cumminsforum.com/forum/ge...ost-turbo.html

Hope it helps a bit.

 

That's exactly the kind of information I was looking for...thanks!

 

I have boh pre & post thermo couplers and they do read different. The Post EGT would normally drop to 300 around the same time the Pre EGT would prior to me installing the Banks Ram Air system. Now the Pre EGT will be as low as 200 long before the Post EGT gets to 300. As a normal rule of thumb you don't want your Post turbo EGT to get any higher than 1100.