Pyrometer - Pre or Post Turbo?

[Stone]

So I'm in the process of deciding where to put my pyrometer in the BJ74. The easiest way would be post-turbo, with a clamp-on probe. I've been told by some people that this is not very useful though, as the temperature readings don't really reflect what's going on upstream at the turbo itself. One diesel tech that I spoke with asked me "why bother" when I told him I was planning on installing a post-turbo pyro.

Seems like it would be a real PITA to install a pre-turbo pyrometer. I took a quick look tonight, and since the turbo sits kind of on top of the exhaust manifold, the most feasible place I could put in the probe would be underneath the manifold just in front of the elbow that goes up to meet the turbo housing. I'd have to remove the exhaust manifold (again) and turbo in order to drill this out and do the install...not really looking forward to that.

So...are post-turbo temp readings of any use, or should I go through all the trouble and do it right and install it pre-turbo? Thanks.

 

[crushers]

what i have been doing is puting it right into the exhaust housing side of the turbo. about 2" from the blades.
on the HZJ75 i installed pre turbo for a try and found that the temps accelerate faster but cool off faster as well, go figure.
anyway, in my mind, the whole idea of a pyro is to teachyou to drive the unit according to how fast the temps rise and fall. if you are running at max temp all the time then it is time to change your driving habits.
pre-turbo i max at 1300, post turbo i max at 1200 , if you set your max at what you feel comfortable with then does it really matter where you install it? it isn't like you will be raceing your truck so just use it as a guide.
as for the butt head that said why bother, obviously he has no idea of the reason why you are installing it.
okay, so that was a bit blunt but then so was he.
it is much easier to run the probe into the exhuast pipe but do it as close to the turbo as possible and make sure the probe tip is roughly 1/2 way through the pipe and make sure you use the fiberglass washer.
cheers

 

[HZJ60 Guy]

I wrote and talked to Safari about their turbo kit for my 1HZ. They told me that their extractors (read exhaust manifold) has a factory built (read drilled) hole for the pyro probe. They suggest installing it there. That's what Im going to do.

TB

 

[dieseldog]

Any pyrometer will be useful; however, the purpose of a pyro is somewhat subverted when it is placed post-turbo. You'll always be guessing if the temp drop across the turbo is really what you think it is. That might give you comfort, but I'm much more comfortable KNOWING what the temp is. There is just too much at stake. I tapped into the exhaust manifold on my Dodge Cummins with the manifold in place. No particular difficulty involved, but I was extremely careful to clean all drill shavings away before tapping the threads. I've never had a lick of trouble since.

 

[HZJ60 Guy]

Any pyrometer will be useful; however, the purpose of a pyro is somewhat subverted when it is placed post-turbo. You'll always be guessing if the temp drop across the turbo is really what you think it is. That might give you comfort, but I'm much more comfortable KNOWING what the temp is. There is just too much at stake. I tapped into the exhaust manifold on my Dodge Cummins with the manifold in place. No particular difficulty involved, but I was extremely careful to clean all drill shavings away before tapping the threads. I've never had a lick of trouble since.

The Dog knows what he's talking about, BUT I still have to advise taking the E manifold OFF when you drill and tap it. To much is at stake.

Just my .07 cents.....


Tom

 

[crushers]

or at least remove the turbo and drill where you can get access to the internal shavings...

 

[cruiser_guy]

I agree with Tom and 'Dog. I know Wayne has different views, 'cause this has been discussed before but I need to be sure I'm not going into meltdown! I can only tell that with a pre-turbo pyrometer reading. I drilled and tapped my AXT manifold before installation and it has not come loose or suffered any damage at all in over two years.

 

[honk]

Along with Dieseldog, my diesel experience is derived from my Dodge trucks with the Cummins engine and my time spent at the TurboDieselRegister.com website. That site is perhaps the largest base of user experience available online, and the concensus there is that the pyrometer probe should be placed before the turbo for the best indication of realtime combustion chamber temperatures.

At least two members of that register have had sudden catastophic engine failures related to combustion temperatures. In both cases they were able to report that the failures occured while pulling heavy uphill with pyro indications in excess of 1300 degrees. Both engines holed the #6 piston dramatically - the entire piston top was found desintigrated. Each happened quite suddenly and both owners reported no previous indication of impending trouble.

From those I think that a 'safe' maximum temperature should be decided upon and strictly observed. Because of the immediate temperature changes which can occur I want to know of them as soon as is possible, and for that purpose my probes will always be as close to the cylinders as possible. I think an ideal setup would incorporate a probe for each cylinder in an engine, but failing that I think that locating the probe at a point where readings can be had for all cylinders generally and with preference given the last in line is best. I see no reason with those engines to exceed 1200 degrees even when loaded since a drop in temperature can be achieved by simply using a lower speed in a lower gear. People who choose to have diesel powered vehicles cannot be in much of a hurry after all.

 

[wesintl]

repost....

https://forum.ih8mud.com/showthread.php?t=37680&highlight=pyro

 

[crushers]

short busts into the red zone is acceptable, it is long term durations that will hurt the engine...

 

[honk]

short busts into the red zone is acceptable, it is long term durations that will hurt the engine...

Yes........probably. And in the episodes I mention each of those drivers admittedly pressed their engines for too long (obviously). But to me the fact of engine destruction is a poor way to define the term "too long". I'd rather avoid the issue by staying out of the red at all times if I can, particularly with these 'baby' diesels .

 

[crushers]

if you want a kick then leave everything stock and go for a boot with the pyro installed, drive as you normally do and watch the pyro climb...

 

[brownbear]

ok, my way of looking at it is different. I say post turbo is fine. The up and down spikes are natural.
The thermocouple is very sensitive. I agree its duration at a higher temps that will be destructive.

But come on- who really thinks that when they did not have a pyro(first 20 yrs of the vehicle life) that this engine did not sit at super high EGT's climbing hills with the driver non knowing... ???
Most 3B's have most likely been up there tonnes of times. So now we are gonna baby it?

If your post turbo just drive it to 1100 max. Yes the turbo does take some of the energy out of the hot exhaust gas, but it isn't gonna lower so much that you can't drive it sensible. You'll still get the feel for when the extended heat builds up.

Stone drill as close to the turbo outlet you can, and read a little lower on the gauge, Otherwise take all the manifold apart and drill. Hey whatever you got time for.

 

[greasypants]

I installed mine pre-turbo on my hj61. Figured I might as well get the most out of my gauge I spend 160 bucks on. After 190000km already on the truck I wondered the same thing, is there any point babying it now after all those years without a gauge. I'm sure the temps have been way up there many times before. My intententions where to use the gauge as a guide to tune the fuel after I increased the boost to 12 psi but decided to leave it alone because I could still reach 1300 going up a hill with the added boost. Wonder how hot it was without the added boost for all those years ?

 

[cruiser_guy]

Greasypants, I was wondering the same thing. I installed my AXT turbo on my '82 BJ60 and was going to play with fuel but I can hit 1300 on a steep hill so I left well enough alone. I'm pre-turbo!

I've had my intake hose pop off the intake manifold (after the turbo) and the EGT's shot up like you wouldn't believe. It has me wondering how things were before I had a turbo!

 

[Stone]

Yeah, Wes...I know. But 7 for pre and 7 for post wasn't exactly decisive.

From the replies that I've been reading, and reading up some more on other diesel pages, I'm leaning towards putting it in pre-turbo. Maybe I'll rent a car for a couple of days so I can have the turbo and manifold apart and not have to rush things.

Thanks for all the advice.

 

[HZJ60 Guy]

No disrespect meant to anyone, but I'd take the advice of places like Safari and other manufacturers myself. They seem to know what they're doing and they have warrenty liability issues to deal with that would tend to lean them to the conservative side. The conservative side would seen to protect your equipment I would think and they are mounting the probe in the exhaust manifold.


TB

 

[Technikev]

I think Wayne pretty much laid it out there correctly, but if you will run up the temps and hold them there for a while, it sure would be nice to know what your EGT really is. That 100-200 degree temp difference between pre and post is the difference between running up the coq at 1100 or 1300. I think that I would like to know an accurate temp.

And I am also interested in knowing the difference if there is one between even a clamp on thermocouple post turbo and one mounted into the exhaust stream post turbo.

Some people on this list go on about aftermarket water temp guages and oil pressure guages in the name of accuracy. Do you really want to rely on a mostly sort of accurate probably close enough if you don't push it too hard pyrometer?

Yeah, post turbo will work just fine in almost all circumstances, but I think pre turbo is the better choice. And maybe worth the extra hassle. Good luck either way.

-kevin

 

[cruiser_guy]

And I am also interested in knowing the difference if there is one between even a clamp on thermocouple post turbo and one mounted into the exhaust stream post turbo.

A clamp on simply measures pipe temperature, like I care how hot my exhaust pipe is?!? That would be the worst choice by far. Almost not worth having in my opinion.

 

[crushers]

if i am reading this right the clamp on pyro is the exact same guage and sensor as the drill and instert. the probe still must be about mid stream to get an acurate reading.
now i might be off in left feild if there really is a mount on the outside of the pipe pyro sensor...
cheers