What is the advantages/disadvantages of running an EGT probe pre turbo or post turbo?
I would think that it would be more beneficial running pre turbo because it is closer to the head. On the down side if something brakes off the probe then it will pass through the turbo.

 

I put mine pre turbo. I want to know the temps the turbo and cylinders are seeing.

And as far as the probe coming apart, I have never heard of the happening. But if it did, it would be an excuse for a bigger turbo, and enough fuel to spool it.

 

I am by no means am an expert.........but I will throw in my .02 worth.......

The 500 hp Cat engine in my Peterbilt has the pyrometer probe in the exhaust elbow after the turbo...............

I would only think that the engineers at Caterpillar would know what they are doing and if it should be before the turbo they would have it installed that way...............

I watch my pyro pulling long grades and then when I am cooling down the turbo before turning the engine off...............

300 degrees is cooled down........
600 degrees is running empty........
900 degrees pulling under normal load
12-1500 degrees heavy load on extreme grade and probably in wrong gear

Not sure how that compares with the little 5.9...........
I have ordered some guages and I will be installing mine after the turbo....right or wrong.............

 

Cummins recommends going post turbo (because they pretty much have to in case of failure). majority of the big rigs are post turbo, not quite for certain why... but 95% of the members here are running pre-turbo and so will i when it is time for me to install gauges...

 

RIATA..... Tell it like it is.

 

What do you mean by "in case of failure"? The event of the thermocouple breaking off into the exhaust path through the turbine.
That's my hunch for having the probe post turbo.

 

The failure rate of thermocouples is nearly nill. They have always had a great safety record, and even better in the last 10 years. While I agree, it does make sense to have the probe after the turbo you cannot accurately monitor EGT's post turbo in short run situations. With some of these guys pushing 1500 degrees in the quarter (or next light, hopefully for a short period of time) they need to know.. right now.. what the EGT's are doing, not after the heat has been soaked up by the turbo & 2 feet of cast iron pipe. Preturbo is the only way to go for the most accurate readings.

JMHO

 

my .02

pre turbo

advantage
temps are closer to the piston

dissadvange
thermocouple faliure destroying turbo

post turbo

advantage
no way to damage turbo

disadvantage
temps are farther away fro the piston

 

I started with post turbo before any mods. But with mods i would go preturbo you will be amazed at temp difference your choice. If you want mine preturbo is the way to go.GOOD LUCK

 

i just did post because im lazy. but going to do pre when i get twins.

 

i did pre because i am lazy... didn't want to do it twice... drilled with engine running, tapped engine dead with lots of grease. that was a year ago.. no problems.. and i'd rather take out a charger if the probe fails than have to tear into the engine to fix it if it doesn't show me what the pistons are getting... [turbo ~$1500, engine +$5000]

 

I have a friend who was running post turbo probe with mods to his truck, he never saw more that 1000*F, which as most people he equated to about 1300* pre turbo temps. I moved the probe to pre turbo for him---and he was easily seeing 1500*+ before he hit 90 MPH.

PRE TURBO is the only way to go!!

 

My question is how accurate are these egt guages? Do they come with documentation from the manufacturer stating that they are "this" accuarate +/- "this" many degrees? How often do they come out of calibration? How do you know that they have come out of calibration? How do you recalibrate them if they do come out of calibration? How do you know if they're reading accuarately in the first place? In my line of work, we have guages breaking or coming out of calibration all the time. We even have an entire department devoted to making sure all the instrumentation in the plant stays calibrated. So you're probably wondering what my point is. It is simply this: You buy an egt guage to watch trend, not actual numbers (to a point, of course). You don't even know what the actual numbers are in the first place (you may be out of calibration). But, if you are running at, 500* indicated for the past 2hrs and then all of sudden your egt jumps up a couple hundered degrees for no reason...well, now you know you have a problem; not because of numbers, but because of trend. I feel it is mostly semantics really. Whether you place the probe pre or post turbo really doesn't matter for every day operations. I'd go with manufacturer recommendations. On the other hand, I can see how for drag racing you may want the probe as close as possible. But then again, you're still just watching trend (when was the last time you checked calibration?), just for a much quicker duration. And how many of us drag race a lot?

 

I have checked mine, we have a simulator at work so I can do this as needed. Our Simulator has to be calibrated yearly in our line of work. We allow +-5*F. When my gauge says 1500* I know it. We also verify the probes, as I have seen them go bad.

 

I think this is where this post belongs.
I have mine mounted preturbo and have noticed that coming down a hill where I live, I have seen the gauge show less than 300.
Is this normal??