NHC 250 Turbo Conversion in M923

162tcat · Jun 13, 2014

Here are a few pics of the dual fuel mod. It's a straight forward project, the hardest part is removing the plug from the rear head. I stole someone elses idea and used lapping compound on the allen head but that still didn't get it. I ended up using a torch to get it very hot then a proto square style easy out and it came right out then. Parts were around $40 from napa and that included lots of extra brake line for my screw ups. There is another thread around here with better pics and lots of info too.

Floridianson · Nov 9, 2014

Yep no A/F screw on nonturbo motors but wonder if you could changed out the PT would there be any gains.

Ops wrong thread

beesonoffroad · Nov 11, 2014

I installed a ntc400 pt pump on mine and piped air from air lines to mimic a turbo till i get one. [thumbzup]

infidel got me · Nov 28, 2014

doghead said:
You should see his daily driver...

I hope that's not an automatic,those sound crappy without a manual shift.

wrenchturner6238 · Feb 16, 2015

I am adding a turbo to my M931. I have read through some of the threads here and I have not seen or missed it in the threads. My question is are the people doing these projects plugging the holes that go into the intake port in the heads when making a non turbo into a turbo engine? These ports are 1/8" pipe (I think is the correct size) they were used to burn the crank case psi. When installing a turbo without plugging the holes you loose boost and build crank case PSI.

wrenchturner6238 · Feb 16, 2015

Ok I have an update to my previous post. I pulled off my intake and checked the little ports for crank case gas re-burn. The holes in my heads were plugged. This would be a good thing to look for at least; for sure if you are having problems like quite a bit of blow by or low boost psi.

jarhead1086 · Feb 16, 2015

Mine were already plugged from going through into the intake as well. Like you said, its a good thing to check while the intake is off. While I'm posting on this thread, I also decided that mounting the surge tank on the drivers side like others have done makes the best sense. I planned on making a custom tank from the beginning regardless which side it went on. I plan on plumbing the return line from the intake cooler to the drain out the bottom of the surge tank. I want to mount it where I still have room to stand by the PT pump. I need to double time this project because spring is here already.

silverstate55 · Feb 17, 2015

jarhead1086 said:
Mine were already plugged from going through into the intake as well. Like you said, its a good thing to check while the intake is off. While I'm posting on this thread, I also decided that mounting the surge tank on the drivers side like others have done makes the best sense. I planned on making a custom tank from the beginning regardless which side it went on. I plan on plumbing the return line from the intake cooler to the drain out the bottom of the surge tank. I want to mount it where I still have room to stand by the PT pump. I need to double time this project because spring is here already.

I wish I would have taken photos of your progress; looks better than OEM!! You'll be more than happy once it's all done & dialed-in. Nice work!

airborneinfantrygrunt75 · May 17, 2015

I recently won an M923 at a gov auction and wanted to place a van shelter on it in place of the bed. I recently acquired the van shelter for it but am kind of stuck over if it will even pull it's own weight being that it is Th 250 engine. My question is have you pulled anything after placing your new turbo conversion and also do you think if I went this route would it work???

wrenchturner6238 · May 17, 2015

These engines were used for every day hauling over the road they did not have the max GVW as they do now but they did there job reliably. Yes with out a turbo it would haul van shelter you would not want to be in a hurry but it will do fine. I have not hauled anything with mine yet I am still in the process of many upgrades but yes i feel it will be worth it to do a turbo up grade and add just a little fuel PSI it should make 20 or a little more HP which will be a good help in my opinion.

jarhead1086 · May 22, 2015

See if these upload. I have more pictures but these get the ideas across. Still need to adjust timing, tranny shifting, and turn the fuel up a little. It won't go much over 800 F where it could hit 1100 F before. Sounds much better in the cab.

Carlo · May 23, 2015

A diesel motor without a turbo just doesn't sound good. I wish I could turbo my 934A1 it's so gutless. Nice work!

rhurey · May 23, 2015

Carlo said:
A diesel motor without a turbo just doesn't sound good. I wish I could turbo my 934A1 it's so gutless. Nice work!

I still hear the turbo spool up and dump in my head, its just wrong not having one.

beesonoffroad · Jun 29, 2015

I got tired of the nhc250 and well pictures are worth a thousand words

grendel · Sep 6, 2015

So, did you blow it?

The 8.3L I have is being donated... I have a NHC250 kicking around, thought I'd throw it into my M931, since it's losing the smaller motor... I can turbo it pretty easily.

Bandit02 · Sep 7, 2015

I have no idea why guys spend their money turboing these engines. If it's just for a whistle, well ok I get that.

The NHC250 is a pile of crap....pile of crap for being utilized into these military vehicles that are the backbone of any armed forces. I wonder why you'd want a underpowered engine in a truck meant to haul weight, such as my M931. Just by itself the 250' struggles offroad going up dirt roads with a 6* incline with being put into 2nd gear and bobtailing....pathetic. Imagine how'd you feel with people shooting at you?!

Guys spend their hard earned money putting a turbo on an engine not designed to run one. No piston cooling jets to absorb the heat on the aluminium pistons and it has a small cam...like tiny, so I have no idea why you'd stick jakes on since it'll wear out that cam out prematurely. Guys stick these things on and they "look" like a Big Cam 400 but they're just not, and when you drive them you know they definitely are not lol.

My truck works. I use a lowboy that hauls equipment and it struggles so bad it's embarrassing even on paved roads. Regardless of what it's spec'd to haul weight these 900 series trucks are tougher and better built then anything that's out there commercially, only thing that keeps me not keeping up to a 2015 Kenworth T600 with a Cummins ISX spec'd to 600 HP is my lil 250' and the diffs gear ratio. Truck-to-truck my M931 will eat any commercial truck out there, not by creature comforts in today's trucks but how well the truck is built for abuse. One thing AM General did right.

My truck runs offroad, If I wanted to line haul equipment on paved highways I'll buy a new Western Star for the comfy ride it'll provide for $180 000 they retail for about. In the 2 years I've had my truck all I've done is oil changes/grease and a couple pinion seals, far far less a new Class 8 truck would need after 2 years running hard offroad on oil patch roads.

Same with the 8.3, you like 240 hp then by all means giver. I'd like to see someone swap the marine version in that runs 450 HP stock, that thing would be a rocket.

But my 250' is 14 litres of crap. I'm searching for a Cat 3406B (which is about the same size - 14.7L) to swap in that rocks 525 hp stock from factory. Guys say the rest of the powertrain won't hold up. Give the Allison a bit of credit. My truck loaded weights in just under 70 000 lbs, waaaaay more then it "should" haul but like I said these trucks are built tougher then most modern trucks minus creature comforts. The engine is the weak point. If I had more hp/tq I'll pull more weight.

I cannot wait to swap in that B model Cat, it'll truly "wake" it up. And see my other trucker friends face when I blow past them on the same roads and not having to stop and chain up becuase I can keep the speed and keep the traction.

I respect the work guys do to their own rigs it looks great! Keep it up.

grendel · Sep 7, 2015

Bandit02 said:
But my 250' is 14 litres of crap. I'm searching for a Cat 3406B (which is about the same size - 14.7L) to swap in that rocks 525 hp stock from factory. Guys say the rest of the powertrain won't hold up. Give the Allison a bit of credit. My truck loaded weights in just under 70 000 lbs, waaaaay more then it "should" haul but like I said these trucks are built tougher then most modern trucks minus creature comforts. The engine is the weak point. If I had more hp/tq I'll pull more weight.

I cannot wait to swap in that B model Cat, it'll truly "wake" it up. And see my other trucker friends face when I blow past them on the same roads and not having to stop and chain up becuase I can keep the speed and keep the traction.

I respect the work guys do to their own rigs it looks great! Keep it up.

A B model 3406 with how much HP stock?

I have 3 of them here, none over 425hp.

Turboing the motor to get a little more out of it is much easier than installing an entirely different engine. You can do it with all stock junk yard parts.

162tcat · Sep 7, 2015

From personal experience, you can get around 335-350 horse safety from the NHC 250 by adding a turbo and doing pump adjustments. The small cam is a non issue unless you plan on exceeding 250,000 or more miles on that rig. Considering most are current under 20k, I don't think that will happen.

If you want that huge mountain climbing power, buy a new truck with 500-600 horse. Even the old "big cam cummins" is a turd by todays standards. Keep in mind, up until the early 90's the majority of freight in this country was moved with less than 350 horse and most still is! Ask your next company driver or cement truck how much he has under the hood, probably less than 350 horse...

silverstate55 · Sep 7, 2015

Most of these trucks won't ever see 100K miles in their lifetimes either; very few are run hard as yours are, Bandit02. It is fascinating to hear of your M931's use, I know there are others out there who run their 5-tons hard, but most of us don't. And from the experience of swapping engines, it's no fun when you find you have to rebuild/repair the donor engine and other pieces/parts, not to mention fabricate new mounts, brackets, linkages, etc... For most, installing a turbo and making it work for their uses is just the ticket, so to speak.

JohnnyBM931A2 · Sep 7, 2015

Bandit02 said:
I have no idea why guys spend their money turboing these engines. If it's just for a whistle, well ok I get that.

The NHC250 is a pile of crap....pile of crap for being utilized into these military vehicles that are the backbone of any armed forces. I wonder why you'd want a underpowered engine in a truck meant to haul weight, such as my M931. Just by itself the 250' struggles offroad going up dirt roads with a 6* incline with being put into 2nd gear and bobtailing....pathetic. Imagine how'd you feel with people shooting at you?!

Guys spend their hard earned money putting a turbo on an engine not designed to run one. No piston cooling jets to absorb the heat on the aluminium pistons and it has a small cam...like tiny, so I have no idea why you'd stick jakes on since it'll wear out that cam out prematurely. Guys stick these things on and they "look" like a Big Cam 400 but they're just not, and when you drive them you know they definitely are not lol.

My truck works. I use a lowboy that hauls equipment and it struggles so bad it's embarrassing even on paved roads. Regardless of what it's spec'd to haul weight these 900 series trucks are tougher and better built then anything that's out there commercially, only thing that keeps me not keeping up to a 2015 Kenworth T600 with a Cummins ISX spec'd to 600 HP is my lil 250' and the diffs gear ratio. Truck-to-truck my M931 will eat any commercial truck out there, not by creature comforts in today's trucks but how well the truck is built for abuse. One thing AM General did right.

My truck runs offroad, If I wanted to line haul equipment on paved highways I'll buy a new Western Star for the comfy ride it'll provide for $180 000 they retail for about. In the 2 years I've had my truck all I've done is oil changes/grease and a couple pinion seals, far far less a new Class 8 truck would need after 2 years running hard offroad on oil patch roads.

Same with the 8.3, you like 240 hp then by all means giver. I'd like to see someone swap the marine version in that runs 450 HP stock, that thing would be a rocket.

But my 250' is 14 litres of crap. I'm searching for a Cat 3406B (which is about the same size - 14.7L) to swap in that rocks 525 hp stock from factory. Guys say the rest of the powertrain won't hold up. Give the Allison a bit of credit. My truck loaded weights in just under 70 000 lbs, waaaaay more then it "should" haul but like I said these trucks are built tougher then most modern trucks minus creature comforts. The engine is the weak point. If I had more hp/tq I'll pull more weight.

I cannot wait to swap in that B model Cat, it'll truly "wake" it up. And see my other trucker friends face when I blow past them on the same roads and not having to stop and chain up becuase I can keep the speed and keep the traction.

I respect the work guys do to their own rigs it looks great! Keep it up.

Ok.. Now I am curious. What is the difference between the street and marine 8.3's? Did they just turn it up and add oil squirters, or is there more involved to reach that 400+hp mark? That would be a pretty cool swap.. I'd do it if I had the money.

NHC 250 Turbo Conversion in M923

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