[quote author=Badunit link=board=49;threadid=23281;start=0#msg219922 date=1070856205]
My only concern is cool down temp of the turbo. Post turbo is for that.
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If you are concerned about cool down temp of the turbo, then post turbo is not the proper location for a probe. On shutting down, you are concerned about heat soaking the oil left in the cartridge. The only true indication of what temperature you are soaking the cartridge with are you pre-turbo temps.

I realize that most heavy equipment will mount their probes post-turbo, however this is simply because boost on heavy equipment is predictable when loaded down. Its almost always set at about 20 - 25 PSI, which probably means about 200 - 250F differential to pre-turbo.

So, on our light trucks, pre-turbo is the only useful mounting spot for a pyrometer.

Rod

 

I am not trying to start an augument but, I do not see how that is possible, the pyro probe only measures the temp of the air going past it not the metal it is attached to, not to say the metal cannot heat up the air. If you want to measure the temp of metal by measureing the air temp around it the only way to do it would be to measure the air after it has passed through it. Think of a wood burning stove, if you wanted to measure the temp of the actual stove without taking the temp of the metal would you put a probe at the air intake or in the flue where the smoke comes out? I do not see how you can know the temp of the turbo if you are measureing the air before it gets to it. I think many times the higher temps seen pre turbo are from the exhaust manifold getting hot and heating the air before it enters the turbo.

 

How does the exhaust manifold get hot?

Merrick

 

[quote author=Bertram65 link=board=49;threadid=23281;start=15#msg224470 date=1071597652]
I do not see how that is possible, the pyro probe only measures the temp of the air going past it not the metal it is attached to, not to say the metal cannot heat up the air.
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As exhaust gasses pass through a turbine assembly, the turbine assembly heat soaks and dissipates heat. Doesn't matter what temperature the turbine is currently at, its still going to heat soak and reduce the temperature of the exhaust gasses as they exit the turbine. Once the exhaust gasses hit the downpipe, the aluminized pipe further heat soaks and dissipates heat. In the first 6 inches of downpipe, you can see 100F-200F of cooling taking place.

So, the temperature of the exhaust gasses leaving the turbine could be higher than the temperature of the turbine assembly itself. Probably not, but you don't really know for sure.

Now, you measure the temperature of the gasses moving into the turbine, before the turbine has had a chance to heat soak and dissipate heat. If these temperatures are at somewhere around 300F, then you can say for certain that the turbine is not going to be heated beyond 300F. Your turbine, once its had a chance to dissipate any stored heat from a hard run, cannot be hotter than the temperature of the gasses flowing into it. So you let your truck idle down to 300F, give it a few more moments to let the turbine assembly dissipate the heat, and shutdown knowing that your turbine and cartridge assembly is definitely going to be at or lower than 300F.

Rod

 

There's a thread out there somewhere from someone who put probes pre and post and watched them both. IIRC the pre turbo probe showed a notably faster change in temperature when the engine went under load. There was also a pretty large variation in the difference in temp with the pre-turbo probe showing temps 300 to 500(+?) higher than post.

However, the post turbo probe temps dropped slowly too. My conclusion was that the exhaust gas itself determines the temperature pre-turbo. No engine load, no big temp rise. Apparently the temperature of the turbo itself has a big impact on the temp read downstream. Again, IIRC the guy with both places measured said that the pre-turbo temps dropped in a few minutes while the post turbo temps dropped 1 to 5 minutes later.

btw - Cummins also suggests post turbo.

 

Install pre-turbo, I did. Turbo can be no cooler than the temperature of the gases entering.

I didn't drop my turbo to drill and tap. Had wheel bearing grees on both drill and tap. Put a log in tailpipe and started the engine just before it broke through. Wear gloves as it is warm. Exhaust gases blow metal chips our as break through takes place. Several of the Diesel shops do it this way without any problems. Afterwards use pencil magnet to check for any chips.

That was 17,000 miles ago and I have had no problems.

 

put mine in post turbo and have had no problems what so ever. I tapped into the elbow off of the turbo just before the down pipe. 8)

 

Rod,
I agree with what you are saying, but for using the pyro for verifying cool down temps I still think the post is as good as the pre. However for monitoring a modified truck while running hard the pre probably gives you a better idea of what is going on in the combustion chamber, in that case the turbo is not in as much danger as perhaps the pistons or other internal engine parts from high temps as they are occuring there.

 

Go pre and be worry free.

Cummins telling you to go post turbo is just their CYA >. They don't sell hop up parts or tell you to do anything that would void warrenty even if you don't have any. They don't know anything other than whats in the service manual or even care for that matter.

I have seen hundreds of large industrial engines with pre turbo pyros and never seen a failure. Valves have broken off and blown past bending the probe and hit the turbo.. The probe was fine and didn't cause any damage, the valve did.

Post turbo for cool down does have its merrits if you are bone stock and are going to be. I tend to agree with that statement for sensing turbo temperature for cool down after the turbo as it is a heat source. There is alot of iron there to cool down before turning off the key.

J-eh

 

two trucks so far,both pre turbo.. one turbo removal-other not
temps mine 1250* hotest, normal 600/900.....

 

I have been on this board for I guess over two years, been reading other boards for longer. I have read of every form of damage and breakdown, but never have I read where the probe burned or broke off and hit the turbo. I have heard stories galore about how it happens all the time, but never the first report of it happening to the writer.

Another non problem is cast iron chips from drilling damaging the turbo. By the time the impeller speed reaches a speed that could be damaged, the chips are long gone. Anyone that worked on two cycle Detroit's are familiar with the damage done when the fire rings break up and spit out through the turbo. The worst damage that I have seen from the rings passing through is some corner chips on the impeller. The exhaust impeller of a turbo is some real tough stuff, you don't hurt it easily. Turbo's are a very simple device. I have changed the bearings out on a 92 series Detroit turbo on the side of the road, and installed a new compressor wheel. A lot of work got done on the side of the road or in a truck stop when out for a month or more.

 

they all got a pre turbo .... all were done with turbo on .... and i have probably done a dozen more for other folks all pre turbo with turbo on ... just laid a bh shop vac next to drill bit and drilled away ... stuck a magnet down there and fired 'er up ... tiny pieces will just blow through the turbine ... i've been reading these sites since they came out and you can always find someone who installed post and later pre only to find temps way in excess of what they were calculating ... if you're gonna have to calculate to get actual pre temps anyway why not just put it there in the first place

 

I just installed mine pre-turbo and didn't need to remove the turbo. I did 3 things....I rigged up my shop vac nozzle right next to where I was drilling (couldn't even see the shavings the vac cleared them away so quickly). I set the regulator on my air compressor to 35psi and wedged an airchuck in my tailpipe with some rags. That way any pieces would get blown back out and sucked up by the shop vac. Lastly, to be thorough, I used my pen magnet to clean any last bits of metal out of the manifold. I think I got 3 tiny little bits stuck to the magnet after fishing around for a couple of minutes.

The change in exhaust temp is so rapid I think pre-turbo is the way to go. That way you can tell more accurately if you are close to 1300 if you plan to bomb. I am amazed how quick that temp goes up when I run it through the gears.

-Muzzy

 

If you call the ISSPRO tech guy, he can tell you stories of probes breaking off and hitting the turbo. As well, another site Ive been on had a first hand story in which the very same thing happened to a member.

That being said, I think it is very rare and is most likely due to improper installation. Mine will go preturbo as this gives the most accurate temperature indication.