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Turbo for NHC250 Cummins?

D6c

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Did a little internet search to see if anyone has added a turbo to a NHC250 Cummins in a 5-ton M939 series truck but didn't come up with anything. Curios if anyone has ever put together a kit.
Is it practical to do, or are there engine limitations that make it a bad idea?
My brother did a 302 in an M135 years ago and it worked.
 

msgjd

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Did a little internet search to see if anyone has added a turbo to a NHC250 Cummins in a 5-ton M939 series truck but didn't come up with anything. Curios if anyone has ever put together a kit.
Is it practical to do, or are there engine limitations that make it a bad idea?
My brother did a 302 in an M135 years ago and it worked.
there is plenty of discussion in the 5-ton forums right here about turbo-ing an NHC250 .. It will be found in the M809-series discussions .. The M939-series came after my "hands-on" army time and I am unsure whether the early non-turbo M939-series engine is same exact engine as the M809-series , but if it is the same NHC250, then yes, there are mild-to-severe limitations to the mod .. It all depends on what you expect to do/haul with the truck.. I am not gonna reinvent the wheel here, there is plenty said in the M809 and perhaps 5-ton Mods forum by the experts who have done it.. Personally, if you expect to haul heavy OTR with it you would be better-off swapping out for a NTC290 if you can find one.. NTC350's are easier to be had but the oil filter can and cooler location might interfere with your frame rail.. I know that can be an issue with the M809-series, been there, seen it
 
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D6c

Member
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IA
there is plenty of discussion in the 5-ton forums right here about turbo-ing an NHC250 .. It will be found in the M809-series discussions .. The M939-series came after my "hands-on" army time and I am unsure whether the early non-turbo M939-series engine is same exact engine as the M809-series , but if it is the same NHC250, then yes, there are mild-to-severe limitations to the mod .. It all depends on what you expect to do/haul with the truck.. I am not gonna reinvent the wheel here, there is plenty said in the M809 and perhaps 5-ton Mods forum by the experts who have done it.. Personally, if you expect to haul heavy OTR with it you would be better-off swapping out for a NTC290 if you can find one.. NTC350's are easier to be had but the oil filter can and cooler location might interfere with your frame rail.. I know that can be an issue with the M809-series, been there, seen it
I did run across one M809 series turbo mod, which looks like quite a bit of work. I use the truck to haul heavy equipment on short hauls (no 4-lane travel)
and would like to be able to pull a hill at more than 25 mph. Probably easier to trade trucks than do the modification.
 

msgjd

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I use the truck to haul heavy equipment on short hauls (no 4-lane travel)
and would like to be able to pull a hill at more than 25 mph. Probably easier to trade trucks than do the modification.
the problem to overcome is the lack of piston coolers in the NHC250.. Guys that run around town for fun can get away with just popping a turbo on there, change the fuel button, and maybe not even put in a pyrometer.. However, anyone pulling hills and loads with the mod has warned about watching the pyro very closely and not being able to put their foot in it except very briefly.. As tempted as I have been to turbo my M817 and M818 that are my main heavy road haulers / mountain climbers, it really isn't worth my time to do the mod and then have to live with the limitations and potential catastrophic damage of the mod

Thus I just keep the heavy-haulers/road-runners in tip-top tune and they get the job done, even if I'm losing time at 25mph getting bored on the worst hills in 5th low , or even 20mph in 4th low... Doing the mod and melting pistons is not an option, even with a pyro gauge.. The hills I pull are lengthy in places, it's a 25-mile climb out of a valley to get loads to destinations at 1600+ elevation.. So when I get on those hills and into the low side, I just remind myself of all the time I lost rolling 112,000#-plus up the hills in the high-peaks of the adirondacks at 20 to 25mph, on interstate, with an 18-speed and 550HP under the hood .. Let's talk about pucker factor on foggy nights or in the thickest of snow storms, and sometimes both at same time, wondering whether or not you are gonna get a sudden high-speed push from behind to quickly end someone's day, perhaps your own too.. It has happened too many times up there..

To remember losing a good 30+ minutes with big power on those interstate hills 3x a day at 20 to 25mph yet logging over 700 miles daily, makes having to live with loaded NHC250's on the hills of secondary roads seem miniscule in my case.. But I still have hope to build a beast or two before I'm gone and time is running out fast.. I have a fresh NTC290 waiting to go into the M817, that's if it doesn't make its way into the S-2574 16yd tandem dump first ;) .. Yeah I know, the 16yd tandem is the more-logical place for it to go .. Better gears, better payload, better on-road characteristics.. But watching the orange flame from the M817's stack at night on the hills is more interesting.. Decisions decisions ..
 
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Superthermal

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Utah, Murray, United States
I have been researching this quite a while and have a couple of takeaways with not having done this mod as of yet.
1. Many comments from others state that after adding a pyro on even a non-turbo'ed NHC250 that the exhaust temperature is way higher than they ever expected and after viewing it they think they may have already done damage to their motor with the "stock" config and their old driving styles. Because the exhaust temps are now being viewed,they modify their driving style to protect their unmodified motor.

2. Many comments from other state that after adding their turbo their exhaust temps actually drop. Now this possible due to the added air being pushed into the engine, however, if your adding more air.... you would like to add more fuel (power) to match. This pushes the temps back up, but even so most have reported better than stock temps even under loads or climbing hills. Even with this "caution" most users having added the turbo are very happy with the bump in power. In my opinion if you are going to add a turbo on the non-piston oilier squirter style NHC250 you should without question add an after-cooler to the intake. This is to me a little added insurance to the already questionable motive of adding a turbo that does not have piston squirters. But to each their own as many have not gone this route.

3. Prior to the Turbo mod, most MVrs add the Dual fuel mod. I did mine and it added maybe some power... Not very noticeable but it is there.

4. The HT3B or HT60 seem to be the choices of a turbo. Most of the comments of those who have had both is they are both an impressive improvement but the HT60 gives better more noticeable lower end power in the range of 1000 to 1600 rpm. So from the comments of others, the HT60 was the one I was holding out for if I choose to go this way.

5. You will need to be touching several other items on your motor, like a new fuel button, Most have a 21, or a 17 and some go as low as a 15. However all of these increase fuel rail pressure which has adverse affects on the cam to injector stress. The lower the number the higher the stress. My rig has stock about 150 PSI fuel rail pressure. For some reason this pressure jumped to 160 when I did the dual fuel mod. Some feel you can safely run up to 200, others feel 220 psi but others feel anything above stock is looking for trouble. To get around changing the fuel button which increases the fuel rail pressure and puts you into this questionable realm of cam/injector stress, some change the injectors in the heads with ones that have a higher flow rate and modify the injection pump to match. This mod makes it UN-necessary to increase the stress on the cam since more fuel can be delivered with the larger orifice on the injectors and the matched flow from the modified PT pump. The wide accepted opinion is these mods are best done by a shop like Pimco. You send them your pump and injectors and they send you a worked over set to the specifications they help you figure out. Those who go this route seem very happy with the mod and it's cost to get it.

6. Depending on the MV 809 or 923 series, You will need:
6a. to modify the exhaust, possibly loosing a muffler all together,
6b. the intake tubing/housing etc... to make it connect to the opposite side of the engine,
6c. turbo oilier to cool the bearing of the turbo,
6d, Plugging the ports in the head
6E. adding a Pyro mentioned above has a preferred by most mounting position to be pre turbo, in the rear exhaust manifold port that is fed by the three rear pistons.
6F. Possible hood modification or bumping up the cab to clear if you have an 809 series.
6G,H,I,J,K LOL I am sure I am leaving something out like moving the overflow for the cooling system etc... Make a list it is long.

That is my take. If I was done with the other mods I am looking at, I would go this route as obviously I am interested. Let us know how it works out for you if you take the "spin". Would love to read about it.
 

Crf450x

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Location
Fall Branch, TN
It’s easy to add a turbo with oem parts that are readily available either new or in junk yards. The lack of piston squirters is the biggest reason to add a turbo as it will significantly lower egts. For some reason a lot of people have that backwards. In a diesel more air=lower temps. You should have an egt gauge on any diesel regardless in my opinion.
With a turbo, you have options…you can leave the fuel stock and never worry about egt again, you can add a moderate amount of fuel and only worry about egt under certain circumstances, or you can go crazy with the fuel and have to stare at a gauge every time you go up a hill.
If you decide to increase the fuel pressure, I’d recommend a gauge for that as well. Being a small cam, you don’t want to get crazy with the pressure.
 

simp5782

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It would be cheaper and wiser to just get a 916. Speaking from experience. A turbo NHC250 is just going to get destroyed internally being worked. You would really want an RG31 MRAP radiator and intercooler to put on the truck to intercool the engine.

You could swap a big cam into the 5 ton but the transmission won't hold up. Plus you have the cost of the big cam and work. 916s can be found running for 3 to 5k.
 

hethead

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Seattle, WA.
Changing trucks is always easiest but if you’re the handy type, adding a turbo with a little boost (10-15 psi) and bumping up the fuel pressure a little (don‘t exceed 200 often or by much) will give a nice, reliable bump in power without raising EGT’s (turbos lower EGTs). Plenty of turbo’d 250s ran long haul back in the old days. Cummins put together a kit for it (long gone). You’ll be around 270-280 hp (and shouldn’t go much higher without piston coolers if you’re pulling weight) but will hold together just fine. The Allison should keep you from lugging it, which is when pistons get hottest. Make sure your valves and injectors are adjusted, and filters are clean first though, if you haven’t already. You’ll need a pyro, fuel pressure and boost gauges (which I think we should have anyway for diagnostics) and a few “button” swaps to get it dialed in so you don’t have to worry about pressures or temps. I love having the turbo on mine.
 

muthkw25

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My buddy turboed his m925a1 and use a hx60 turbo with a mrap intercooler and radiator. Lifted the cab and hood 2 inches. He also installed a methanol injection kit. He had his pump build by premco and had a #20 button installed and also 20% over injectors by premco. I can tell you from first hand account that the temperatures are significantly decreased. He had a trailer weighing over 6klbs with 16r20 tires and his truck pulls fantastic and saw 700 degrees F for temps with 10lbs of boost. Highest boost he see's is 15lbs. Methanol kit also makes a huge difference with cooling the air, cleaning the cylinders, and increasing horsepower.

Granted he doesn't beat on the truck or hasn't put it under a huge load yet, but the truck runs fantastic and has no issues with heat and has been reliable. I think most of the time people blow these engines up is when you add too much fuel pressure to the cam, too high egts, or over revving the engine.
 

hethead

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Seattle, WA.
In case anyone was wondering, here are the Cummins turbo "smoke kit" settings from Cummins bulletins.
Thanks for these. Useful specs. From what I understand, the smoke kits were "encouraged" to clean up the stacks and required the mechanics to add the turbo, but turn down the fuel. Giving the same power with less fuel/cleaner exhaust. Guys would come back later and get the fuel turned back up to get another 30 or 40 hp. Which is what the truckers really wanted from these kits anyway.
 

hethead

Active member
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Location
Seattle, WA.
My buddy turboed his m925a1 and use a hx60 turbo with a mrap intercooler and radiator. Lifted the cab and hood 2 inches. He also installed a methanol injection kit. He had his pump build by premco and had a #20 button installed and also 20% over injectors by premco. I can tell you from first hand account that the temperatures are significantly decreased. He had a trailer weighing over 6klbs with 16r20 tires and his truck pulls fantastic and saw 700 degrees F for temps with 10lbs of boost. Highest boost he see's is 15lbs. Methanol kit also makes a huge difference with cooling the air, cleaning the cylinders, and increasing horsepower.

Granted he doesn't beat on the truck or hasn't put it under a huge load yet, but the truck runs fantastic and has no issues with heat and has been reliable. I think most of the time people blow these engines up is when you add too much fuel pressure to the cam, too high egts, or over revving the engine.
This about a 45k trailer (with a 20k tongue weight on the pintle). Only had to go about 100 miles so not like a long test, but temps were great with 10 psi boost and 180-200 psi fuel pressure under load. No crazy grades but there were a few hills. I was about 65k on the scale. Wouldn't want to do it often with this set up. This much weight really needs a fifth wheel, but the job got done.

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