GaCamper

I know this is a subject that has been talked about over & over again. I know some mount it the probe pre-turbo & some mount it post-turbo. I mounted mine post-turbo. Every Diesel motor that I have seen Cat, Detroit, Cummins etc. in the big trucks, the probe is always mounted post turbo.
I was just wondering if anybody has ever talked to "Cummins" to see where they recommend mounting the probe. ??? This came up among a few friends of mine and just thought I would ask.

wannadiesel

No diesel OEM recommends mounting the pyro pre-turbo. They don't want to assume the risk of a pyro probe going through the turbo. I have never seen a post from anyone who claimed this happened to them, it's always friend of a friend stuff. That said, a big truck diesel is going to run a lot more hours at high EGT than any Cummins in a pickup, so I think the risk in heavier applications is much higher.

Alec

What dave said is right.

The reason I decided to mount my probe pre-turbo is once you start tinkering with the engine, ESPECIALLY changing the turbo housing, you have no idea what temps the pistons are seeing relative to your post turbo temperatures. If you have a stock engine, the manufacturer knows what the temperature difference is accross the turbo for a given set of circumstances and can then set a maximum safe operating temperature, but here I'm running a 12cm housing and a stock exhaust, Monty is running a 16 and 4" stacks, Bushy was running a 14 on an hx35 (actually, he may have only had it on his H1, but you get the idea).

We can't compare truck to truck. Heck, you are worried about your pyro going through the turbo? We lost three gasoline engines to spark plug electrodes falling off (okay -- bent valves and scored cylinders, but all in all as much or more PITA than replacing a turbo). It can happen, but it mostly doesn't.

Pittsburgh injection claims they put 'em pre turbo on all their hopped up class 8 engines.

Of course, as someone else pointed out, if you start messing with your valve overlap, you really need a probe in the piston crown, because you can blow enough fresh air through the valves to cool down your exhaust while the pistons are turning into molten aluminum and coked oil . . .

The point being, it probably doesn't matter, as long as you are consistent.

Bob Beauchaine

I wanted mine mounted where it would give me the hotest reading - I don't want to guess what my EGT's are. To me it's the same as mounting you auto transmission temp guage on the return line - you don't get the hotest temp reading so you really can't adjust your driving to prolong your CTD life or tranny life.

Bob

Lil Dog

To put the mind at ease, the industrial engines I work with have pyros and are all mounted pre turbo, that is that they usually have one per cylinder as well as 1 preturbo. These things last over 40,000 hours (most Cummins only last 10,000) and can take alot of abuse before they would cause damage to the turbo.

Pre turbo is the way to go if you are at all modifying your truck. Talk to Bushy, when he started out it was post turbo, but after the bombing bug hit, it had to go pre turbo.

J-eh

frostie

I have mounted my pyro stinger post turbo as you have done.
I have been a diesel mechanic for over 20 years. I did mine post turbo cause that is the way it has been done in the trucking industry for as long as I can recall.
This is a matter of knowing how far to go with the temp. I would not go past 1200 degrres post turbo for any length of time. The fact is I lied. I have gone to 1400 on 2 different occasions and would not recomend you try it.
If you install your stinger pre turbo, then you are only checking 3 cylinders out of 6. if you have a cylinder getting hot on the wrong 3 then you will never know it.
Lildog and I disagree in this subject. He mentioned in a response, in the past, that the truckers mainly use the pyro for cool down time. This is not the case. I know many truckers who have the fuel cranked very high and have to watch there pyros so as not to melt there engines down.
This subject is a matter of preference and knowing your limitations.
It is best that you stay under 1200 post turbo.
If you prefer pre turbo than you will have to ask those who run preturbo.

GaCamper

frostie,
Now that is the first time I ever heard that. Your saying mounting the probe pre-turbo you only messure temp on 3 cylinders. Little confused on that one.... ??? Mine me asking why only 3 cylinders?
I maybe be thinking wrong here, but my thought was that the exhuast coming out of the turbo would give a truer reading of what the turbo temp is. Once the exhuast leaves the cylinder and travel through the exhuast manifold to the turbo, the exhuast is loosing temp. So the exhaust temp would be lower by the time it enters the turbo.
An from what I'm gathing from the other post, being the others are modifying thier motors, with the probe pre-trubo it sounds like they are more concerned about cylinder heat. ???
I guess to do it right and not worry would be to mount probes both pre & post turbo......
It just as puzzled me why most all diesel engines have the probe post-turbo and with the smaller diesels in our pickups there's such a big fuss about being pre-turbo. All diesels funtion about the same other then when you start modifying them.

Monty

When I first started, I mounted the pyro post turbo. Highest temp I saw was 1000*. I am a diesel mechanic for Freightliner and yes every one that i have seen was mounted post turbo. But, after talking to the guys that should know in this business, Piers, Joe Donelly etc. I quickly moved mine to pre turbo. After moving it, at those same conditions that I was seeing 1000*..it was actually 1400-1450 degrees. Big difference I will say. So, basically I could get a 250* to almost 500* degree difference at times.

Its a matter of personal preference I guess, but why take the chance? I dont want to monitor how hot the turbo is, I want the temp straight out of the combustion chamber.

FWIW: test engines for different mfg's all have pyros pre turbo and usually one per cylinder.

HammerMTB

Virtually all diesel OEM's reccommend mounting the pyro probe post-turbo. They also reccommend you not modify in any way. If you were to leave your CTD stock, a post-turbo pyro would be fine. You'd likely have little use for it.
When you start to BOMB the engine, the pryo probe mounted post-turbo will "fool" you. The temp rise will seem modest. You'll think you can go hotter. It would be a mistake. The reason is, the turbo uses both exhaust flow and heat to drive the shaft. So, some of the heat that was in the combustion chamber is used to drive the turbo faster. You will only be able to measure this heat with a probe pre-turbo. If you're going to BOMB, you need the probe there.
The reason you only measure 3 cylinders pre-turbo is that the exhaust manifold is divided. The turbo entry is also divided. So, you can measure the front 3 or the back 3. I chose the front 3 because years ago when we were doing some development, we found that #1 gets a little less intake air (in a 12 valve, anyway) and it's the most likely to heat up soonest.
Something to let your mind chew on.... 8)

GaCamper

Thanks for all of the good information. Now give me your thoughts on this setup. On my truck it's pretty much stock. I'm not wanting to built a hot rod out of it. I've had the fuel turned up some & I built a Propane Injection system which I only use when I need the extra power. I've added a K&N Airfilter and working a modification for the air box. I don't believe I'll be doing any other mod's to the motor. With my pyrometer probe being post-turbo I should be ok? Right!
The reason I'm asking I have a friend that is wanting to do the simliar setup to his truck.

The Old Man

GaCamper - - My 2cts worth, (which is probably worth only 1.5cts ). Go pre turbo. Do it right the first time and you won't have to do it again. It sounds good to say you don't want to make it into a hot rod but once you get started you're in deep trouble. Something else always looks interesting to try. I'm not a mechanic, (I need advice just to change a light bulb :'(), but I would think using propane for only a couple moments would make a tremendous difference in temps. When mine was post turbo, before any mods other than the 16cm2 housing, the temps seemed to go change slowly. Once moved to pre turbo the fluctuation was dramatically faster.

Yeah, go pre turbo and have fun.

Pat

frostie

Again, there is no right or wrong way to do it.
As Monty said the pyro is not to measure turbo temp. but you want to know how hot your aluminium pistons are getting in the cylinders. You dont want to start melting parts.
As Hammer said if you go pre turbo than it would be best to put the probe in the front section of the manifold do to #1 cylinder will probably run the hottest.
I no the limitations on my set up being post turbo and have gone beyond what I should have. but that was my choice.
My engine still runs fine with 253K miles
You just need to have a set number in your mind of how hot you will let it get and not go beyond that figure.
Enjoy the bombing. ;D

hdm48

OK, so I get a call from a guy who just bought an EGT guage from NAPA and he wants to know where the probe should be located.
So I told him his two options.

BUT, being an engine builder and tuner I had to give him the run down on the BEST location in order to get an ACCURATE reading on exhaust temps.
I know,I know, you all think you know where it is supposed to go. BUT, where it SHOULD go is 6 inches from the face of an exhaust valve. And the probe 'tip' has got to be in the CENTER of the manifold or port in order to read properly.Plus, you need to find the hottest running cylinder and mount it to read that one.
SO, where it needs to be is mounted on the outside wall of the number 6 cylinder port just before (actualy about 2 inches from the flange)the number 5 cylinder enters the manifold.
I don't know why I am writing this. I just needed to vent I guess. A guy I built an engine for just fried it tonight at the Monroe indoor flat track race. WHY? Because it got cold and he didn't rejet. He has an Optac EGT meter (high tech and expensive, I know, I have one too) and he did not look at it.
If you're gonna put the guage in, LOOK at it!!
OK, I'm done. The drugs are taking effect.

Dave

Bushy

There is both sides to this topic and both are correct in general terms...
I ran post-turbo for quite some time... Initially I saw temps around 1000*F running roughly 18-20 psi boost.
As the boost went up so did the temps. I thought I'd be ok if I used the rule of thumb formula for estimating the actual temps... 10*F for every 1 pound of boost...
Well, it did hold some water so to speak..that is until I started seeing 25, 28, 30, 35 psi boost.
Only after I moved the probe to the pre-turbo location did I see the actual temps...
Up to the 22-24 psi range the "formula" was pretty close... but at that point it started to go astray on me...
I found that running 30psi boost on a posted 10% grade 1/3 mi long my actual temps were 350*F or more out...
The higher the boost the larger the "error"..

I also have not heard of anyone breaking off a probe tip and having it or any part of it , ruin a turbo.
The issue of which cylinders you should "sample" is open, in my opinion as well.
For example, some think that the rear 3 cylinders (4/5/6) run hotter, others think the front 3 run hotter.
In the big scheme of things, and this is only my opinion here, what difference is 50*F or 100*F going to make if you are up that high to worry about it...???? In the end, if you really want a true "average or mean" temp reading, why not mount the probe on either side of the manifold web and make a hole in the web to allow exhaust gases to mix.... personally I would not go to that extreme or risk myself. (risk as in weakening the web's structural purpose)
Maybe this is a test I'll do in the future. I have a probe hole on either side of the web now. I was intending to do some "drive pressure" testing but perhaps this test should be done as well....hmmmm.....

Pastor b0b...

hdm48

When anyone asks me why I put the probe pre-turbo, I tell them it is so you can see both the true exhaust temp and what you are putting into the turbo.
And like Bob, in 40 years of racing every kind of fuel powered toy, I have never seen a probe fall into the turbo from heat. That does not include engine parts running into it though.
When we would run a new engine set-up for the first time on a water dyno we always ran a temp probe in each cylinder just to get an idea what the flow (in/out) is doing inside. Some times we would alter valve timing or lift or even a change in lash adjustment for that cylinder.
But my point is this, where ever you put the probe, know what is good and what is bad and LOOK at it once in a while.

Believe it or not, my step father had a EGT guage in his ford and didn't know what it did.
Doesn't that make you wonder how many people out there do the same?
I trully believe, for people like this, there are gas powered trucks.

Dave