More Power From NHC 250 in M939 Series Trucks With Allison Transmissions

[jarhead1086]

I found this while trying to find out how to plug the vent holes Hasbeen was talking about. 3% derate per 1000 ft elevation would explain why she was so tired at 7000 ft going through southern Utah. I remember seeing this in another post but found it in print and thought to stash it here.

In the NHC250 era, some applications needed a way to supply more air to the
engine to help eliminate black smoke problems, especially in higher
altitudes and Cummins developed a turbocharger 'smoke kit'. The kit included
all the components required to install the turbocharger on the engine, as
well as information about required changes to the fuel pump and injector
settings that increased engine horsepower from 250 to 270 hp. Some Cummins
distributors may still have the Service/Parts Topic that provides the
details of the 'smoke kit'.

According to Cummins Service/Parts Topic 73T10-1 dated January 1973, Cummins
Service/Parts Topic 72T18-1 dated June 1972 contains comprehensive details
of ratings, fuel pump codes and specifications/part number of the
significant components of all recent NH and NT models. These topics indicate
that naturally aspirated engines should be derated 3 % for each 1000 feet in
altitude.

We also have a more current bulletin no. 3379020-00 dated April 1975 titled:
NH220/230 and NHC250 Turbocharger Conversion Kits. This bulletin has
comprehensive part numbers, instructions and information about components
and changes required to install the turbocharger smoke kits on these engine
models. Your local Cummins distributor should have this bulletin in their
files and can determine if the parts are available or if current parts can
be used.
If the above topics are not available, then the Cummins distributor may want
to refer to Cummins parts catalog 3379590-00 dated March 1979. This parts
book covers the Cummins Small Cam NT-855 model engines for automotive
applications which includes NTC-250 and NHCT-270 engines.

 

[Jakelc15]

That info is from here
http://www.mil-veh.org/archives/03-08/0724.html

Was also referenced in Jwallers 818 turbo install thread. Pg. 15

http://www.steelsoldiers.com/showthread.php?28133-818-now-with-turbo-and-pics

I've been trying to get those old bulletins from Cummins. They seem to be on paper only. If someone stops in a Cummins store they would probably Xerox it for you.

 

[jarhead1086]

Thanks Jakelc15. That is a long read but a lot of good pictures. Grateful to have the extra room in my 923 after seeing all that. I found the pic of that breather hole. You could poke a wire down the hole and see if it comes out in the intake or not. Sounds like there might be some of both out there. I will check my breathers now since I have time on my hands. My local Cummins dealer may let me borrow a copy of this bulletin to PDF and post. They are an easy going group.
I bought brand new aftermarket pulse manifolds to go with the new turbo and had them coated by HPC coatings in SLC with 2000 F titanium ceramic. I hate the rust. The ones from the junk yard were all cracked and leaking or very corroded. Now I am debating taking the plunge to stainless exhaust. Long run for me out the back so I can start it in the garage without a fan. I am divorced so I don't have to worry about that tongue lashing, but my kids may need shoes and Christmas is coming up. 5" stainless is really expensive and it doesn't come in green or tan.

 

[Jakelc15]

I tried to get those publications from Cummins. No luck. Here's their response.

Cummins Inc. does not have copies of the requested publications in our archive.

Regards,
QuickServe Online Customer Support
Cummins Inc.

 

[jarhead1086]

I did not have to plug my breather holes since they did not go through into the intakes. I also checked a few old school Cummins shops and could not get copies of these pubs but I won't give up looking. I have my intercooler installed and the turbo all hooked up. I will start working on the cooling system after I get my front crank seal replaced and radiator put back in. I am debating about putting the intercooler on its own system by using a tranny type cooler out front, an electric pump, and another small fill reservoir. This would allow for a lot more cooling without using 180 F engine coolant. No experience here just thinking while its tore apart. I worry about an oil cooler going out and making the disaster bigger by getting in my intercooler too. Hmmm? Any thoughts from people that know.

 

[Jayco36REQS]

Ok.. maybe off topic a tad... but I saw this and got me thinking more on the use of a mixed blower/turbo combo....

http://www.ebay.com/itm/1947-cat-di...D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

 

[patracy]

I'm running a 17 button now and checked pressure. Normal crusing I was seeing around 150-170psi at load under speed. Romping on it, I'd see the gauge twitch slightly passed 200psi. EGTs are still at 900F max. Boost is a max of 15psi.

 

[Major Asstyrd]

Trucks usually use air-to-air charge-air coolers (also called aftercooler or erroneously, intercooler). If it has an intricate structure of aluminum "turbulators" in the charge-air tubes which transfer heat to the outer structure so it can be removed by outside air, they are efficient. A good cooler can take 350 degree compressed air and turn it into 120 degree air before it goes to the engine. This more oxygen-dense, which is the objective. Less EGT and smoke. Air-to-air coolers don't have fluid to leak. But they can crack, so it's good to pressure test them every year or two if driven a lot. Original equipment and some aftermarket truck coolers are of a tube-and-fin type and these can crack where the tubes are brazed to the thin header plates, and also crack at the weld between the plates and the end tanks. This is because of the rapid temperature changes every time the accelerator pedal is pushed. They flex. Also it's a chassis part and even rubber-mounted they are stressed. OE coolers usually have a one year warranty for these reasons. There are aftermarket bar-and-plate coolers with much better durability because those two failure modes are not present. They are often cheaper than OE coolers.

If I was going to add a cooler to a non-cooled truck and there isn't a cooler available for that chassis, I'd first try to find an existing cooler that can be adapted. Find a decent size match, the bigger the better, and look for the inlet and outlet pipes to be in good locations. Then mod the brackets and fab some pipes, rubber boots, and clamps to work. Here is a place to download an aftermarket catalog that has diagrams and dimensions of various coolers for commercial trucks. Their part numbers with an "HD" in them happen to be the bar-and-plate types.
http://www.av-tekk.com/catalog.html

 

[ryanaubra]

Pulled a locked-up 250 out of a 925 tonight. Picking up my 290 tomorrow. I will start post when i get something to post. I have a cummins certified mechanic doing the work so i will keep everything as up to date and informative as possible for all of you thinking about doing the swap.

 

[ColtRice17]

any news?

 

[ryanaubra]

About What?

 

[ColtRice17]

the 290 swap how is it going?

 

[ryanaubra]

Oh. Sorry. I have a thread going. I changed direction due to time constraints and added a turbo to a 250 for now. I am going to do the 290 in another truck now. 250 is running good getting ready for suspension and crew cab next.