Rod meyer

When I first got my truck I ran my probe post because my friend that works for freight liner said thats where to put it. As my need for speed progressed and the injectors and box went in I started getting concerned about temps. So now I have both pre and post. Normal driving about a 100 degree difference.WOT a little less than 300 degrees. If your stock go post if your worried. But like already said, if you bomb for safety of your truck go pre. the heavier you fuel you'll be glad you did.

ftltmp

That same engine in a big truck will have 100 more hp.Why do you think your exh temps will be higher than a rig pulling 80,000 @ 70mph. I promise you cummins put that engine through every test possible.The ten years I have been building trucks they have all been after the turbo.Cat ,Detroit, Cummins,and Mercedes.

RustyJC

Excuse me??? There are 450 BHP 5.9L B-series Cummins in Class 8 tractors? Ummm....I don't think so. You might want to check out the 5.9L B-series engine ratings in the Ford F-650 or Freightliner FL-60 or FL-70 - the ratings are lower than a stock Dodge Ram!

A 380-390 flywheel BHP 5.9L diesel is stressed much more highly than a 450-500 flywheel BHP 14L diesel. The smaller engine, in addition to having more BHP/cubic inch of displacement (higher brake specific output), will have a higher BMEP (brake mean effective pressure). Stock big rig engine practices don't automatically apply when we're talking about BOMBed Dodge/Cummins.

Rusty

thumper 549

FTLTMP,
If you go back to the time b4 computers you will remember guys mounting mirrors to see the stacks,,egt guages were usually mounted after the turbo back then cause everyone thought the tips would break off and go thrue the blades .
the" big cam and small cam" are 855 cu in eng.....modern math says they should put out 1 hp per cu in safely and reliably.......that said all class 8 trucks are built with a large safty margin and heat sink abilities.
Now take the little 5.9 and ask more of it then mom ever thoght of putting out ,somthing has to be monitered.!......after all ,,tell me at what temp dose aluminum MELT!!
If you go on repeating "what the book says" we would still be told this can't be done!.........So,please add a box to you 5.9 and some other mods and tell us how it goes,,,
Trust me read my sig. we do not put guages in for looks
I could go on and quote thermodynamics and nomenclatures and impress you with my vocabulary,,,but were all feinds here and thats not the pt. We are tha Borg of collective knowldge ..use it or learn on you own....
I am done

NORM

can a thermocouple under the collar read hot ?

RustyJC

Norm,

I hope no one is getting hot under the collar. After all, we can disagree without being disagreeable, right?

Rusty

Push Rod

I'm almost scared to get into this thread. My background is heavy diesel (agricultural, and heavy truck) and had these same questions when we first started modifying the 5.9s. My thought process ran along these lines as well, but time has proven that Cummins, Cat and other heavy engine builders do not take into account modifications to the engines. For a given fueling level, with a given displacement and turbocharger, pre and post thermocouple temperature differences are predictable. ESPECIALLY in heavy trucks, since the boost is usually low, or at max (approx. 22-25 PSI, depending on engine).

Once you modifiy the engine, either with fueling or additional air, changes in timing, or simply a new turbocharger with a different efficiency map (even if you're running the same boost levels), the differential between pre and post is no longer predictable. A rule of thumb is 100F for every 10 pounds of boost, however, like most rules of thumb, I've seen this violated as well. On the heavier powered vehicles, 500 HP+, I've seen differentials of 700F between pre and post. This has been tested with dual thermocouples in the pre and post locations.

So, in other words, ignore what the factory engineers are telling you. If they feel that post-turbo thermocouples are acceptable on MODIFIED engines, they haven't been in the same room as a modified engine to see what the differences truly are. If you're running a stock engine, with stock fueling, go ahead and mount post-turbo, and use 1000F as your max values. But as soon as that engine is modified, your 1000F value is blown out of the water.

Rod