Engine/Transmission (1998.5 - 2002) Pre and Post Turbo EGT questions

[NoSeeUm]

I have a Pre and a Post EGT T/C installed. The Post is installed the Banks Brake T/C port. The Banks Brake is a bigger hunk of metal than the stock elbow.



What I notice is the amount of temperature that the turbo pulls out when running with boost. I see Post turbo EGT 200-300F cooler at times at high boost and around 100F at low boost. This pretty much makes sense to me, is it about normal?



Another thing that I notice is the cooldown time between Pre and Post. I am going to say that it takes 3-5 times longer to have the Post EGT drop below 300F than it does the Pre EGT. Typically unloaded, the Pre temperature can already be cooled to 250F and the Post can still be in the mid 300F range. After stopping when pulling a load, the Post temperature can still be in the mid to high 400F range as the Pre temperature goes below 300F. In any case, the Pre temperature drops fairly quickly and Post temperature takes much longer to drop and just creeps down. This normal?



Another thing that I managed to find out is when I did a 5th to 4th down shift running loaded and pulling a pretty good grade. In 5th my EGT was creeping to 1150F so I down shifted. I was traveling 60 MPH at the time and I wanted to see the performance at the same speed. Man-o-Man the EGT's skyrocketed, especially Post as my boost pressure dropped very low. Immediately afterward Pre EGT slammed to 1350F and Post EGT almost matched it. Its like the higher RPM flushed all the heat out of the engine, and there was alot of it. Maybe I barked the turbo, I don't know for sure. For sure, I won't ever try that again.



Thanks in advance;

Jim

 

[nps]

It all sounds normal to me. Pre-turbo is recommended for one TC because, as you have seen, that is where you will see wider and faster variations in temps. Plus, after you get past the turbo, there's nothing to damage anyway.

 

[isb360]

Getting a faster response out of pre-turbo gauge is expected because there is no "delay" caused by the turbo which is acting like a heat sink/heat extractor, etc. When you back off the throttle, fuel drops to almost nothing meaning your engine is essentially an air pump pushing lots of cool air through it. The delay in seeing the post-turbo gauge drop is attributable to the heat sinking into the turbo and then being released again when not under load. This is analogous to when you are under hard acceleration (say drag racing) and you hit 1400-1500+ EGT's but only briefly --- won't damage any components because there is no time for heat to sink into them.



I am intrigued that you saw HIGHER egt's when you downshifted. All things being equal, a lower gear, higher RPM and higher boost means more air going through for the same power demand on the engine (i. e. same speed on highway under same conditions pulling same load). I see you have a PM3 stacked with Smarty, so there may be some timing things happening there that are affecting the EGT's with your downshifts.



Good post!

Tim

 

[NoSeeUm]

OK thanks, armed with a little more knowledge.



It pretty much has been the standard for me to let my EGT cool to 300F minus before I shut off the engine. I did this under the assumption that I was cooling my turbo down adequately. Now that I have the Post EGT T/C I am almost certain that just watching Pre EGT drop to 300F still leaves some pretty hot components. I run dino oil so I always worry about coking.

I am intrigued that you saw HIGHER egt's when you downshifted. All things being equal, a lower gear, higher RPM and higher boost means more air going through for the same power demand on the engine (i. e. same speed on highway under same conditions pulling same load). I see you have a PM3 stacked with Smarty, so there may be some timing things happening there that are affecting the EGT's with your downshifts.

Yeah, it was probably the TST adding fueling that spiked me up. The TST has a few second time delay before defueling activates. I had been running the TST high defuel temperature (post turbo) at 750F. This worked pretty well, because it would defuel back to stock before the Pre Turbo EGT got to 1100F.



But... .



As usual I have a problem leaving well enough alone and was experimenting by raising the TST high limit. I am starting to think that during the shift to 4th my speed dropped. I accelerated pretty rapidly back to 60 MPH, thats when I noticed my temperature problems. Weirder still, right after that I shifted back to 5th and pulled the rest of the grade. Pre EGT stayed right around 1100F as normal.



I also think I have issues with my wastegate set-up. It will only sustain 23 psi pulling a load, but will spike to 30 psi under hard acceleration only (empty or loaded).



Jim

 

[Extreme1]

The post EGT is the one to watch for shut down. If you shut down with the turbo too hot the oil will coke in the bearings. (Oil and bearings doesn't like that). I run my EGT on the pre side and my Isspro Turbo Temp Monitor on the post side. That way it never shuts down hot or holds me up waiting.