Pyrometer Question(s)
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Mountain Pass
Joined: Oct 2004
Posts: 243
Likes: 2
From: Kremlin, Ok
Pyrometer Question(s)
Right now, I have a 3" single needle pyro. haven't bought the wire or the thermocouple yet. As much as I'd like to, I can't really afford a dual-sweep pyro. Will I be ok to put the thermocouple in just one side, instead of both. What is the best place to put it? In the pipe right after the exh manifold, or can I drill the manifold without it cracking? I thought about the Y pipe where it comes together, but I'm afraid the exhaust would have cooled down too much by time it gets to that point.
If it was a turbo, I'd put it at the turbo inlet. I am one of those people that do believe in the 300-400 degree difference in the pre and post turbo temps.
If it was a turbo, I'd put it at the turbo inlet. I am one of those people that do believe in the 300-400 degree difference in the pre and post turbo temps.
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
The best location is in the rear of the exhaust manifold.
Not easy to do with the engine installed, but it can be done.
The pistons are the first thing that high EGT's damage, so you want the thermocouple as close to the pistons as possible.
Also with the thermocouple mounted farther from the exhaust manifolds, you have to start calculating how much heat the exhaust has lost so you can calculate how hot the pistons are getting.
More calculations means more chances for errors.
Case in point, pre turbo temp is about equal to post turbo temp plus 300 degrees.
So if the thermocouple is in the manifold and you see 1200 degrees, the thermocouple after the turbo would see 900 degrees in round numbers.
If the round numbers are off, you then see round numbers when you replace pistons.
Usually a squiggly number followed by "several" very round zeros.
Sorry, I have been working on two computers with virus infections for a friend of mine for two days.
I am getting a little wierd with my brain processes right now.
Not easy to do with the engine installed, but it can be done.
The pistons are the first thing that high EGT's damage, so you want the thermocouple as close to the pistons as possible.
Also with the thermocouple mounted farther from the exhaust manifolds, you have to start calculating how much heat the exhaust has lost so you can calculate how hot the pistons are getting.
More calculations means more chances for errors.
Case in point, pre turbo temp is about equal to post turbo temp plus 300 degrees.
So if the thermocouple is in the manifold and you see 1200 degrees, the thermocouple after the turbo would see 900 degrees in round numbers.
If the round numbers are off, you then see round numbers when you replace pistons.
Usually a squiggly number followed by "several" very round zeros.
Sorry, I have been working on two computers with virus infections for a friend of mine for two days.
I am getting a little wierd with my brain processes right now.
Thread Starter
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Mountain Pass
Joined: Oct 2004
Posts: 243
Likes: 2
From: Kremlin, Ok
Right on the money as normal, Dave. I'm thinking the same as you are. I just didn't know if I could drill the manifold and not have to worry about cracking, or if I should put it in the pipe where it joins the manifold. I am fully aware that I wan't it as close to the combustion chamber as possible. I haven't touched my fuel screw in the pump yet, and I refuse to until I have a pyro where I can get some baseline readings first. Might fix the F150 and see if I can trade it for a 6BT. Going to run the trusty ol' 6.9 as long as I can though. It has 273000 miles (maybe 373000), on it, and I'm getting tired of burning a gallon of oil every 200-300 miles. CDR is good.
So do you think it would be fine to run off of just one bank of cylinders, or do you think I should save my pennies and have a pyro for both sides? Maybe I can run two thermocouples for one gauge, by running it through a DPDT switch. hmm, got to do some more research. Thank you Dave.
So do you think it would be fine to run off of just one bank of cylinders, or do you think I should save my pennies and have a pyro for both sides? Maybe I can run two thermocouples for one gauge, by running it through a DPDT switch. hmm, got to do some more research. Thank you Dave.
Senior User
Joined: Sep 2007
Posts: 317
Likes: 0
From: Snohomish, WA
I drilled and tapped mine in the back of the driver's side manifold, in the truck. I took the turbo cross-over pipe off when I did it, and vacuumed out the shavings. After that I ran the truck with the cross-over pipe off to blow out any remaining shavings in the manifold, then re-installed the cross-over pipe.
I didn't have too much problem drilling and tapping with the manifold installed. I thought I would, but it turned out I had enough room to get it done. I would think a non-turbo set up would be similar.
I used to have my thermocouple installed just after the turbo, and while the post turbo temps were lower than the in-manifold temps, what I found more striking was how much the turbo buffered the changes in EGT seen at the manifold. With the thermocouple installed after the turbo, the EGT didn't fluctuate much, but with the thermocouple installed in the manifold, the EGT changes directly with the throttle. Given that it is the spikes in EGT at the pistons that we are interested in, installing the thermocouple after the turbo does not make much sense to me. I can see the benefit of having a second thermocouple installed after the turbo to measure the temp of the turbo, but that would mainly let me know when the turbo is cool enough to shut the truck down (not really super important to me).
I didn't have too much problem drilling and tapping with the manifold installed. I thought I would, but it turned out I had enough room to get it done. I would think a non-turbo set up would be similar.
I used to have my thermocouple installed just after the turbo, and while the post turbo temps were lower than the in-manifold temps, what I found more striking was how much the turbo buffered the changes in EGT seen at the manifold. With the thermocouple installed after the turbo, the EGT didn't fluctuate much, but with the thermocouple installed in the manifold, the EGT changes directly with the throttle. Given that it is the spikes in EGT at the pistons that we are interested in, installing the thermocouple after the turbo does not make much sense to me. I can see the benefit of having a second thermocouple installed after the turbo to measure the temp of the turbo, but that would mainly let me know when the turbo is cool enough to shut the truck down (not really super important to me).
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Posting Guru
Joined: Sep 2007
Posts: 2,207
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From: Las vegas
I drilled mine in the back of the manifold on the passanger side with the engine in the truck I had to notch my inner fender to do it but was able to reinstall the pice I cut out so it has an acces panle. Right befor the drill punches threw i just started the engine so as i drilled threw it would push the shavings out.
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Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
With a pre turbo pyrometer, just let it idle for a minute after the pyrometer drops below 300 degrees and you will be fine.
The easiest way to tear up a turbo is shutting the engine down right after pulling a big hill.
The turbo is so hot it cooks the oil in the turbo, which then blocks the oil passages.
Under driving conditions, the turbo can handle more heat than the pistons can.
The easiest way to tear up a turbo is shutting the engine down right after pulling a big hill.
The turbo is so hot it cooks the oil in the turbo, which then blocks the oil passages.
Under driving conditions, the turbo can handle more heat than the pistons can.