age old question ... pyrometer
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age old question ... pyrometer
I have seen this question posted and answered a many of times, where to hook the pyro up at - post or pre turbo ??? I have mine set up post turbo, being the downpipe was pre-tapped for it there. But, I have seen on here where everyone says pre-turbo. So, here is the dilema, I am in the pressure washing business, and have been cleaning OTR tractors all week, and have noticed on everyone of them that had a pyro, that the E.G.T. probe was sure enough, in the down pipe. So, I got to asking a few of the maintenence guys about it, and thier response was the pyro was to monitor the temp's coming out of the turbo, to keep from burning it up, not out of the exhaust itself, seeing as there will always be " a fire in the hole". Makes sense to me ... i think 
. Now, not saying this is right or wrong, but it was hooked up like this on Pete's and K/W's, and I would lean towards following thier ways of doing things, after all, these are really big diesels. So, the million dollar question is ... post or pre turbo ??? Your thoughts, or experience's with it hooked up in one or the other location's.
. Now, not saying this is right or wrong, but it was hooked up like this on Pete's and K/W's, and I would lean towards following thier ways of doing things, after all, these are really big diesels. So, the million dollar question is ... post or pre turbo ??? Your thoughts, or experience's with it hooked up in one or the other location's.
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From: Seattle
Since the pre-turbo measures temperatures before they get to the turbo, not after the turbo has soaked up some of the heat, your reaction time to back out of it may prevent damage to the engine. I have noticed that pre-turbo you can see immediate results of "foot-in-the-throttle", (or out of the throttle, as case might be).
If you're pulling a hill, trying to pass the slow guy now and then you might just need to pay close attention to the temperature that is going into the turbo as you are trying to squeeze that last bit of performance out of your engine. Now with it post-turbo you may be a little late on backing out of it because; 1) the turbo heat soak may slow the temperature reading, 2) adding up in your mind the 300* to get your max temperature may slow you down a bit.
I think putting it pre-turbo is worth the small amount of work involved – it ain't tough.
Thats just MHO
If you're pulling a hill, trying to pass the slow guy now and then you might just need to pay close attention to the temperature that is going into the turbo as you are trying to squeeze that last bit of performance out of your engine. Now with it post-turbo you may be a little late on backing out of it because; 1) the turbo heat soak may slow the temperature reading, 2) adding up in your mind the 300* to get your max temperature may slow you down a bit.
I think putting it pre-turbo is worth the small amount of work involved – it ain't tough.
Thats just MHO
Posting Guru
Joined: Feb 2004
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From: Elverson, PA
You are NOT trying to protect the turbo by watching your EGT's - that is just the side benefit. You are keeping your pistons from getting too hot.
I don't know jack about OTR trucks - so I can't comment on what they do for pyro - but for me - it is well worth the effort to have a pre-turbo setup that is giving me a real temp reading.
I don't know jack about OTR trucks - so I can't comment on what they do for pyro - but for me - it is well worth the effort to have a pre-turbo setup that is giving me a real temp reading.
Posting Guru
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From: Buckingham, IA
Smokin,
Thanks for the info about the OTR trucks placing of the pyro thermocouple. I never would have guessed that they put it there. For what it's worth, on farm tractors, the probe is placed pre-turbo. But these tractors run under full throttle and high load for prolonged periods of time, like hours, so they are frequently running up near the high temp limit and a slight increase in the load could be just enough to start softening aluminum. The sooner that you can see the increase in EGT the better in this situation. But seldom are PSD's put under these conditions, unless you are trying to pass that stupid ****** who is speeding up as you are trying to pass while pulling the trailer...............
Thanks for the info about the OTR trucks placing of the pyro thermocouple. I never would have guessed that they put it there. For what it's worth, on farm tractors, the probe is placed pre-turbo. But these tractors run under full throttle and high load for prolonged periods of time, like hours, so they are frequently running up near the high temp limit and a slight increase in the load could be just enough to start softening aluminum. The sooner that you can see the increase in EGT the better in this situation. But seldom are PSD's put under these conditions, unless you are trying to pass that stupid ****** who is speeding up as you are trying to pass while pulling the trailer...............
Posting Guru
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From: Elverson, PA
Originally Posted by farmdad
But seldom are PSD's put under these conditions, unless you are trying to pass .......
Unless you have a chip. I have to watch my temps any time I have my chip on the high setting - but I can get it over 1200 even on my low setting if I keep it on the floor for a little bit.
Fleet Mechanic
Joined: Feb 2004
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From: River Valley AR
I also don't know jack about big trucks but maybe the metallugy is different in the pistons. They seem to run 500,000 all the time. IMO the whole idea of using a pyro is to indicate the temp before it's too late, or to use as an economy guide. If you're trying to drive by the pyro for economy, it won't matter where you put it. If you're trying to protect the truck, why not look at the temperature at it's highest and quickest responding point? That point would be pre-turbo IMO.
Posting Guru
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From: Buckingham, IA
Cat-man,
I meant the conditions of prolonged lugging. But you are right about being able to hit 1200*. I've watched the pyro on my son's truck and that needle does move a lot.
Smokin,
Would there be a substantial difference in the amount of air that the turbo is moving in an 18 wheeler as compared to a PSD? And therefore, the size of the turbo? Those motors are twice the displacement so they need a lot of air. Maybe the turbo's are more "oversized" compared to those on a "consumer vehicle"? Just a thought.
I meant the conditions of prolonged lugging. But you are right about being able to hit 1200*. I've watched the pyro on my son's truck and that needle does move a lot.
Smokin,
Would there be a substantial difference in the amount of air that the turbo is moving in an 18 wheeler as compared to a PSD? And therefore, the size of the turbo? Those motors are twice the displacement so they need a lot of air. Maybe the turbo's are more "oversized" compared to those on a "consumer vehicle"? Just a thought.
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FTE Leadership Emeritus
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From: Cabot, Arkansas
If you're trying to protect the truck, why not look at the temperature at it's highest and quickest responding point? That point would be pre-turbo IMO.
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Originally Posted by farmdad
Cat-man,
I meant the conditions of prolonged lugging. But you are right about being able to hit 1200*. I've watched the pyro on my son's truck and that needle does move a lot.
Smokin,
Would there be a substantial difference in the amount of air that the turbo is moving in an 18 wheeler as compared to a PSD? And therefore, the size of the turbo? Those motors are twice the displacement so they need a lot of air. Maybe the turbo's are more "oversized" compared to those on a "consumer vehicle"? Just a thought.
I meant the conditions of prolonged lugging. But you are right about being able to hit 1200*. I've watched the pyro on my son's truck and that needle does move a lot.
Smokin,
Would there be a substantial difference in the amount of air that the turbo is moving in an 18 wheeler as compared to a PSD? And therefore, the size of the turbo? Those motors are twice the displacement so they need a lot of air. Maybe the turbo's are more "oversized" compared to those on a "consumer vehicle"? Just a thought.
Fleet Owner
Joined: Jun 2004
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From: Rio Rico, AZ.
Originally Posted by smokin redneck
Granted, they are of substantial size, my brothers Freightliner has a N-14, 14 litre, and the turbo spools up around 45-50 p.s.i., and it is a garret turbo. Oddly enough, the e.g.t.'s seldom hit 900, thats with 40k in tow. IMHO, I am guessing it may be the application as far as to where the thermocoupler is mounted at and what type of driving is done ... in my truck, I have it mounted post turbo, and the highest I have seen the temps so far is 625, 650 maybe for a brief second, and thats with or without the programmer. Oh well, may have made for interesting post
Fleet Owner
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From: Rio Rico, AZ.
Originally Posted by CAT_man_963
Unless you have a chip. I have to watch my temps any time I have my chip on the high setting - but I can get it over 1200 even on my low setting if I keep it on the floor for a little bit.
Junior User
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From: San Jacinto, CA
pre-turbo placement
Does it really matter where you place your probe in the exhaust manifold scheme ? I've read up pipe (which is a bear to get to if you have to drill and tap). crossover pipe, exhaust manifold etc. etc. ....So since I will be installing an autometer gauge in the near future, it seems to me that the best and easiest place on my 2000 Exc. PSD would be on the drivers side exhaust manifold just before the crossover pipe connection.. What Up ???????
Junior User
Joined: Oct 2004
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From: San Jacinto, CA
show me
Originally Posted by FoMoCo136
I put mine in the exhaust manifold where it is almost sticking in the cylinder. This is to me the best place. If you think about it,,it wont get any hotter than there.