pyrometer placement

[carrk]

Okay guys here is tonight's question:

Just exactly where is the best placement for the thermocouple looking at the exhaust gas temp? I personally think it is best placed upstream of the turbo; however the argument against that is that the thermocouple eventually burns up and ends up in the turbocharger exhaust wheel. End of turbocharger.

I have always thought that the exhaust gas loses energy as it crosses the vanes of the compressor; this is where the transfer of the energy from the exhaust gas to the compressor takes place. Necessarily there is also a temp drop as this takes place. The kicker here is what the pressure drop is across the exhaust turbine. If there is not very much pressure drop across the turbine then there should not be much temperature drop either... this from observing the behavior of high-pressure gasses as they flow across a choke on offshore production wells.

So the real question becomes how much of a pressure drop is there across the exhaust turbine... independent of the loading friction of the compressor turbine? And finally, just how much risk of trashing a turbo is there if I place my thermocouple upstream of my turbo?

I thought this would be a lively discussion forum... and I want to know what the consensus is before I install my gauges!

 

[Diesel Freak]

your concerns have been very well documented throughout the board. I drilled and taped my exhaust manifold for the thermocouple right before the turbo... . this is hotter than the turbine outlet. the temperature difference across the turbine can be as high as 600 F depending on modifications

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http://www.mudrunner.sites.cc

 

[carrk]

As a new member, I tend to forget about researching previous posts on any particular subject. Sorry 'bout that...

 

[HC]

I'm almost afraid to state my opinion - this topic is up there with "synthetic vs. regular oil" in it's ability to bring out some strong opinions on both sides. So I'll just say it this way: When reading the old posts, don't just count the number of "votes" for each option - read the reasons behind the votes, and decide which ones are in line with your goals and beliefs...

 

[MikeR]

It all depends on how modified or stock your truck is going to be. My truck is capable of pushing into 1400+ degrees,so naturally I put it before the turbo.

-Mike

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'00,2500QC,4x4,LWB,Dark Garnet,6spd,3. 54lsd,SLT,DD stage II,Psychotty air,Jacobs ebrake,Isspro pyro & boost gauges,2wd-low,Airoquip fuel lines,Smittybilt nerfs,BFG 285/75 AT's,Midland cb,Clarion 6-disc changer,10-level PM3,Reese 5th-wheel hitch

 

[JB @ C and L Machine]

I agree with Mike R

 

[Mike Vonada]

My $0. 02, drill and tap the manifold. It gives you a more accurate reading. As far as the thermocoupler burning off and dropping into the turbo, never saw a documented incident of that happening. If you are concerned, change the thermocoupler every few years or at least check it. Doesn't take anything to pull it out and look at it.
Good luck!
Mike

 

[RAPID RICK]

If pre turbo is sooooo good why don't the engine mfg. & big truck mfg. drill & tap the
exh. manifold instesd of placing the thermocouple after the turbo. I personally have never seen a Frieghtliner,Kenworth,Volvo
-White etc. with Cummins or Cat motors any other way than post turbo. Rick

 

[illflem]

Pre-turbo is the way to go. Talked with a Banks engineer a while back,he said he's never heard of a thermocouple coming apart and doing damage.

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95' 25004X4,AT,Driftwood,Banks Stinger,Warn fender flairs and running boards(Play truck)95 3500,5 speed,Driftwood,Banks&Phscotty,34,000 GCVW apple and tractor hauler(work truck)

 

[Deezul1]

I have heard that aircraft engines have the thermocouple pre turbo also, they apperently are not worried about turbo failure

 

[RAPID RICK]

Banks doesn't build Cummins & last time I looked my Ram didn't have wings.
Rick

 

[JR2]

I put my thermocouple before the turbo because I knew I was going to bomb to levels that could melt some important parts. So now I can keep an eye on it. If you know you are not going to do any bombing and are just doing this for turbo cool down then after is fine. My eventual plan is to do both. If you are unsure of which to do, I would pick pre-turbo and leave your options to bomb open.

Just my . 02 worth.

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John D. Rathert Jr.
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01 2500 SLT+ QC LWB 4x4 Auto 3. 54 rear end, Forrest Green Sport with all options avail DC Nerf Bars, DC Grill Gard, DC mud flaps, Line-X bed liner, Leer 160XL Topper, Power Edge, EZ Edge, SPA Boost/EGT Gauge on pillar mount, DDT's torque converter - valve body combo and 275 injectors.
4" Exhaust on deck. Air box mods and a new turbo in planning stages.

See My Truck

Dads truck: 98. 5 3500 SLT QC LWB 4x4
Brother Truck: 92 W250 SLT CC LWB 4x4 (Dads old truck)

See 5 Diesels and a Gasser
Winter fun: 2000 Skidoo Summit 700

 

[AWCopTX]

Hey Rapid Rick,That is cool. The last I looked my Ram did not have any wings and was built by Dodge. I also agree with you on placement of that temp probe.

 

[Wiredawg]

Here's my two sense: I tow heavy and need to have accurate exhaust temps. I drilled/tapped exhaust manifold. I'm planning on installing a post one to monitor
cool downs.

Wiredawg



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2000 4X4 SLT QC 8' bed; 6 spd, 3. 54 ; BD exhaust brake and 4" exhaust syst; TST PM2; Airlift Super Duty rear air bags; RS 9000 shocks; pyro/boost gauges in 2 gauge a-pillar mount; back preasure gauge mounted under dash; KN air filter; Brown's Welding brush/grill guard, rear bumper & headache rack; nerf bars and aluminum roll top rear cover, Warn front receiver and Hadley air horns, 20K Reese hitch.