Looking for EGT on NHC/NTC

[acme66]

Almost ready to dump everything we know on burning out the 250 Cummins motors but I am trying to gather one last bit of info. I am looking for pyro numbers from other members. Would love the temp and where your probe is either as measured from the center of the exh manifold or in relation to the joint where the cast iron meets the pipe. Happy Father's day to you all.

Ken

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[wcuhillbilly]

My NTC/NHC 250 has been turbo'd with NHC 350 parts.-manifold, intake etc.
I see 900-1000*F when pulling, estimated 60K gross truck trailer and dozer. Empty is about the same on the hills.
Idle is around 200*F
Pyro is mounted approx. 2.5" downpipe of the turbo. (couldn't get the plug out of the manifold)
Down pipe is 5" for approx. a foot then reduced to stock 4" pipe.
Turbo is a - 4LHR Schwitzer
Truck is: M816 Wrecker- 36,000lbs
PT Pump button is #17 (originally #36) and yes the fuel was turned up by soldier c... I have defueled it some to bring it back to a good spec.

 

[acme66]

Nice. I get 1200 easy with steady acceleration empty then i back out of it. My probe is in the cast iron one inch up from the lower joint where the pipe joins.

Ken

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[red]

Currently non turboed with the pyro mounted into the manifold a little before it's flange on the m816. When driving I keep it below 1150 but if I don't pay attention it will easily go to 1400F (not good). Fuel was turned up before I got the truck, haven't opened the pump to find out what button or how many shims were added since it will spin to 2500rpm while driving.

 

[acme66]

Crap those are numbers I am seeing too. I have never let mine go above 1250 but I could see how it could get there fast. Considering your manifold is shorter I bet piston temp is about the same. That can't be good for them and I don't have the fuel up. Ever found a chart from Cummins listing temp for the 250? Drawing a blank but still looking

Ken

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[red]

Crap those are numbers I am seeing too. I have never let mine go above 1250 but I could see how it could get there fast. Considering your manifold is shorter I bet piston temp is about the same. That can't be good for them and I don't have the fuel up. Ever found a chart from Cummins listing temp for the 250? Drawing a blank but still looking

Ken

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Maximum rated temp at the exhaust manifold collector is 1200F with the mostly aluminum alloy pistons in the nhc250, 1150F is safer for extended high temps. The different alloy temps used in the other 855 series engines (335, 350, 400, etc) tolerate higher temps.

Backing off the throttle, downshifting, installing water/methanol injection, or a turbo are the main options to get the temps cooler. Turbo drops the temps about 200-300 degrees without raising the fuel.

 

[acme66]

It is our belief after killing three 250s that the real culprit is egt despite the often cited liner pitting. I think the issue much worse on the 939 trucks because the automatic allows lugging. I am hoping to gather more egt numbers from 939s but what I see on mine is scary given what we are doing with it. Also experiment with larger intake and exhaust to see if more airflow helps. When done I will put everything we found up here...then replace the 250 with a C series 12 valve like I should have done 4 years ago.

Ken

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[red]

First try manually down shifting to keep the rpm's in the 1600-2100 range, that's where the 855 series engines are happiest. Slow speed offroad driving is where the nhc250 beats the 6cta (and the 8.3 needs even higher RPM's to get the power or else it will build EGT's even faster/hotter).

 

[acme66]

Is the 8.3 as prone to torching pistons or does the turbo keep it cool enough?

Ken

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[acme66]

As for shifting, I am on motor 4, we already do that.

Ken

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[red]

Is the 8.3 as prone to torching pistons or does the turbo keep it cool enough?

Ken

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So long as the 8.3 is kept in it's main RPM range (2000+) then the turbo will help keep it cool. Below that the turbo isn't spooled up yet and not really helping anything. Your slow speed application isn't ideally suited to the 8.3 without some other upgrades (compound turbos).

If you're in the right RPM range then try opening up the exhaust. In most applications the 855 series engines have a 5 or 6" exhaust system, compared to the 4" that these trucks use. Trip to a large truck scrap yard would be the cheapest way to get the air filter box/intake plumbing and the exhuast from a semi. Next step after that is a turbo (working up the price list).

 

[wcuhillbilly]

Acme:
sounds like you need a multi speed tranny, If your still running mine/back country tours at Elevation, the 5 speed trans, whether manual or auto isn't going to make the engine happy at all. Dropping a 10spd or the 16 speed Cat tranny in there will allow you engine to stay at a happy RPM while allowing your road speed to be what the customers want.
Also,, what is your water temps doing.??? Electric auxiliary fans to cool the radiator may be an option for those slow long hill climbs. Kinda like the air fan clutch on the big rigs.

 

[acme66]

On the actual tours the egt is OK with one grade climbing to 1100 but the majority between 800 and 1000. Water temp never seem to rise much and sometimes on the morning runs the fan never kicks on. Makes me wonder if a lower thermostat could force egt down. Haven't thought about that before. What kills us is the 7 miles up to where the tours start. Given how hot egt is on that especially now that I watch like a hawk it is crazy how hot it must have been before. I bet 1400 at times. I am sure that cooked the liners and rings. Btw, looks like just pulling the cap off the intake dropped egt while climbing by 50 degrees. I will know for sure after a few days of comparison. Pulling the stack loose at the air box seems the same as just no cap. I wonder if one of those huge combine prefilters would flow better and extend main finger life. Would look kinda stupid up there.

Ken

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[acme66]

On reflection the tour egt can get higher. I backed out of it Saturday night with 20+ on the truck at 1180. Depends on heat load and elevation. Weekends in July and August could have seen brief periods of 1300 in previous years.

Ken

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[wcuhillbilly]

Turbo,
I pulled the manifolds off a scrap NTC350 and run the watercooled intake, minus the watercool portion. When I put it all together I had the mini radiator pressure tested and it leaked, Minimum of $1000 to get a new one and no way to take it apart to fix it... THus I have a HUGE intake... This has helped to cool mine down. Sorry no number as I didn't have a pyro on until after the turbo and intake.... I can say that after pulling a 6% grade at 60K(dozer truck and trailer) my naturally aspirated 250 would run rough and buck when I got to the top. After the Turbo it cools off immediately, climbs to speed faster and overall runs cooler longer.
my air can is mounted on the pass fender and runs about 18" directly into the turbo.. from the turbo there is a pipe that runs over the engine to the huge intake,,, all of this is helping to cool the intake air before it hits the pistons.

if you have swapped out 3 engines thus far... I would start looking for a small cam 350 or a moderate big cam out of a commercial truck to swap in... you can swap over your 24v stuff onto that civy engine with little trouble, and you will likely gain a Jake brake and more power aside from the Turbo..

 

[acme66]

Jakes would be awesome. Almost had a 290 from a pusher bus but just missed it.

Ken

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[wcuhillbilly]

Turbo that 855, you will wonder why you didn't years ago... the 855 is a lot better engine than the 8.3 for what your doing.. the 8.3 survives only because the Allison trans compensates for the smaller engine.

heres a pic of the intake and turbo... and the jakes(orange piece ontop of rockers.



This is in an 809 body,, you will have a lot more room under the hood of the 939

 

[acme66]

So the Jakes don't lift the valve covers more than an inch or two then?

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[wcuhillbilly]

about 2.5-3" above the rockers

 

[wcuhillbilly]

Thread for my install of the Jakes and Turbo on my wrecker- 816

816 Jakes and Turbo