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

[stuntmog]

Sorry, just got in. I only know enough to be dangerous! Go to a Cummins shop with engine CPL/ serial, type, etc and they can tell you. You wouls also need an intercooler as well to get 350 hp.

 

[Rkrug]

Got my second fuel line installed today , Makes a huge difference! Idles a lot smother and quieter,and has more power when driving also emits a nice smoke trail. Hardest part was getting the fuel rail plug out, tried the allen key but it stripped out so I had my uncle weld a nut on and it came right out.Will post more pics soon.Might get a video of it running to.
Going to go drive it some more now!

 

[patracy]

Got my second fuel line installed today , Makes a huge difference! Idles a lot smother and quieter,and has more power when driving also emits a nice smoke trail. Hardest part was getting the fuel rail plug out, tried the allen key but it stripped out so I had my uncle weld a nut on and it came right out.Will post more pics soon.Might get a video of it running to.
Going to go drive it some more now!

Glad to see you also saw the same results as I did. I'm going to copy your post over to the dual fuel line thread as well.

 

[Csm Davis]

How hard is it to remove the doghouse?

 

[bchauvette]

subscribed

 

[Rkrug]

How hard is it to remove the doghouse?

Not to hard, if a 16 year old like me can figure it out you should be able to too.

I have a winch tower in my truck ,you have to take it off first,there are 2 exterior bolts holding it on and three screws holding it on to the shifting column use a ratchet with a screw driver head to get the screws out because there not quite enough room for a screw driver, after removing the winch tower, remove the shifter tower top from the tower and disconnect the cable and 3 wires ( label the wires),after removing the top unbolt the tower from the fire wall. Now if there's any thing else bolted or screwed on to the fire wall ( fire extinguisher) remove it as well. Now you should be able to remove the top layer of insulation with the hard outer shell. Now pull back the flooring around it to reveal the floor bolts there should be 16 bolts all the way around some are hidden behind insulation which you might have to trim. To reach the bolts behind the dash use two or three ratchet extensions. Once the bolts are all out you should be able to pull the section out. While you have it out trim notches in the insulation where the bolts go through to ease in installation.
Hope this helps.

 

[Jakelc15]

https://quickserve.cummins.com/qs2/pubsys2/xml/en/procedures/99/99-850-020.html?q=+category:service%20language:en^2
Timing cover gaskets.

 

[patracy]

Bumping this back up again. I have my turbo and intake installed on my "SEMTT". I'm going to start changing out the buttons after a test drive. For those of you who have already turbo'ed/button'ed a 250. What button did you end up running? What EGTs are you seeing? Also what EGT are you seeing at idle?

 

[162tcat]

#20 button here, egt around 980 under load.

 

[162tcat]

Also, no smoke so I could probably drop to a lower number.

 

[patracy]

What turbo are you running? Pre turbo I assume?

 

[162tcat]

I'm currently running a T50 from a 335. I was running a HT3B but it was tired and needs a rebuild. Didn't really notice a difference when I switched other that no burnt oil smell. Next plan it to run an air to air IC and bump the power a little more. I don't see and reason why it wouldn't be reliable at the 335-350 power level. With an auto, it's almost impossible to lug the engine at WOT which is where you'd have an issue.

 

[patracy]

Finally went for a test drive. I haven't touched the button yet. But I'm seeing 900F under throttle 5th gear, unloaded. Around 12psi of boost. I think #20 is the "highest" button I have. I'll probably try that next.

 

[162tcat]

Sounds about right. I think 20 is about the best balance of power and reliability. I haven't done much testing but I would imagine when you get into the lower numbers you'll have to be more aware of your EGT gauge while towing or pulling a long hill.

Have you added any shims to the governor? I pulled 3 or 4 out of my parts pump and installed them in mine. Free rev is around 2300 and WOT shift is around 2100 with much more power than before. It used to fall of right before it would shift.

 

[patracy]

I checked #20 is the coolest button and #7 is the hottest I have. I'll try the #20 first. If I stay under 1k on temp and 20psi I'll call it done. I've done the dual fuel line mod as well. No change of shims. I can already rev it to 2300 or higher.

 

[Jakelc15]

Anyone put a gauge on their pump and see what kind of fuel pressure they're getting?

 

[patracy]

Anyone put a gauge on their pump and see what kind of fuel pressure they're getting?

I'm thinking about checking with my local hyd shop to see if they have something and a 1/8" hose to check mine with.

 

[M215]

If I stay under 1k on temp and 20psi I'll call it done.

What are your thought about maximum boost on a turbo equipped NHC250? I find that our M813 hits 12-15psi before hitting 2,000-2,100 rpm for shift points (especially 3-4). So I end up shifting around 1,800 rpm or letting up on the throttle to reduce boost. Is 20 psi boost safe when pulling under heavy load?

 

[patracy]

I would say 20psi is max. But I have an automatic.

 

[patracy]

I swapped in a #20 button. Stock was a #30!