NHC 250 Turbo Conversion in M923

WillWagner · Sep 7, 2015

JohnnyBM931A2 said:
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.

Heads, cooling system, fuel system and exhaust. 400 hp rated C series are mainly found in rec vehicles. They were pushing 500 out of the mechanical C for marine in recreational apps. Automotive was rated at 325 max for trucking.

Hey Bandit, can you tell me why Cummins went from that small, like tiny, cam to the big cam?

Bandit02 · Sep 7, 2015

grendel said:
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.

If I buy a new Cat Reman from my Finning dealership here in town and they will do the pump/timing work to 500 hp. The dinger is it's an extra $3500 but I keep the warranty as long as they do the pump work.

grendel · Sep 7, 2015

Bandit02 said:
If I buy a new Cat Reman from my Finning dealership here in town and they will do the pump/timing work to 500 hp. The dinger is it's an extra $3500 but I keep the warranty as long as they do the pump work.

It may be semantics, but that's not a factory configuration.

How much for a stock B model Reman? I may be interested and 425hp is more than enough for me.

JohnnyBM931A2 · Sep 7, 2015

WillWagner said:
Heads, cooling system, fuel system and exhaust. 400 hp rated C series are mainly found in rec vehicles. They were pushing 500 out of the mechanical C for marine in recreational apps. Automotive was rated at 325 max for trucking.

Hey JohnnyB, can you tell me why Cummins went from that small, like tiny, cam to the big cam?

Hmmm.. Interesting. I wonder if I could find one of those laying around somewhere..

I'm a little confused though.. What engine number would I be searching for to try and find one out of an RV, etc.?

Bandit02 · Sep 7, 2015

grendel said:
It may be semantics, but that's not a factory configuration.

How much for a stock B model Reman? I may be interested and 425hp is more than enough for me.

With taxes, pump work/labour, freight here to me it's about $26 XXX all said and done.

Another option is finding a B model out of a truck or whatever and sending it to them for the pump work. No warranty obviously. But I roll the dice with anything used.

Boy oh boy, I'd love to stuff a K block in there but I doubt it fit LOL.

WillWagner · Sep 8, 2015

JohnnyBM931A2 said:
Hmmm.. Interesting. I wonder if I could find one of those laying around somewhere..

I'm a little confused though.. What engine number would I be searching for to try and find one out of an RV, etc.?

Dunno, there were 100's of thousands of mechanical C's made, still making them for non lead emissions areas of the world. One would need to find a book for the C8.3M version.

If you install the head from an M version on an on road of construction type of engine, you will have smoke and power issues, the swirl factor cast into the head is different due to the cooling abilities and load factor of the M series. Turbos are raw water cooled. You can put the marine injectors in one and do some tweaking with the pump to get more power out of an on road engine. RVs were rated at higher HP than a regular on road application because they don't run daily like a truck, less probability for a failure.

Bandit02 · Sep 8, 2015

WillWagner said:
Heads, cooling system, fuel system and exhaust. 400 hp rated C series are mainly found in rec vehicles. They were pushing 500 out of the mechanical C for marine in recreational apps. Automotive was rated at 325 max for trucking.

Hey Bandit, can you tell me why Cummins went from that small, like tiny, cam to the big cam?

I can guess that the lobes are bigger, producing longer ramping events. Strength & less wear as well.

JohnnyBM931A2 · Sep 8, 2015

WillWagner said:
Dunno, there were 100's of thousands of mechanical C's made, still making them for non lead emissions areas of the world. One would need to find a book for the C8.3M version.

If you install the head from an M version on an on road of construction type of engine, you will have smoke and power issues, the swirl factor cast into the head is different due to the cooling abilities and load factor of the M series. Turbos are raw water cooled. You can put the marine injectors in one and do some tweaking with the pump to get more power out of an on road engine. RVs were rated at higher HP than a regular on road application because they don't run daily like a truck, less probability for a failure.

Yeah I am sure I COULD swap in the injectors, etc., but I would rather not attempt that with a regular 8.3. It would be better just to swap in one that already has 400+hp, and then sell my other engine (or keep it as a spare.) Of course, that's only if I happen to win the lottery in the near future... :roll:

I found a rebuilt 425hp 8.3 on eBay.. Price was $14,000 :shock:

Bandit02 · Sep 8, 2015

14k isn't bad for a rebuilt. I'm sure there's some guarantee behind if it's done professionally. 425 hp in a 8.3L is pretty sweet power to weight ratio.

That thing would blast off to the moon.

JohnnyBM931A2 · Sep 8, 2015

Bandit02 said:
14k isn't bad for a rebuilt. I'm sure there's some guarantee behind if it's done professionally. 425 hp in a 8.3L is pretty sweet power to weight ratio.

That thing would blast off to the moon.

I don't know... seems pretty steep to me. Then again, I'm used to somewhat smaller engines, and not diesels. It might be better if I find a used one at some point and redo it myself. Doing a quick search found exactly 0 available, but I will keep looking. I would rather not spend almost twice as much as I paid for the truck just to get an extra 150hp or so.

162tcat · Sep 8, 2015

Swap out the after cooler for and air to air intercooler, add egt gauges then bump it up to 350 horse and call it a day. Probably less than a grand.

JohnnyBM931A2 · Sep 8, 2015

162tcat said:
Swap out the after cooler for and air to air intercooler, add egt gauges then bump it up to 350 horse and call it a day. Probably less than a grand.

Yeah.. Maybe I should just do something like that.

Bandit02 · Sep 8, 2015

JohnnyBM931A2 said:
I don't know... seems pretty steep to me. Then again, I'm used to somewhat smaller engines, and not diesels. It might be better if I find a used one at some point and redo it myself. Doing a quick search found exactly 0 available, but I will keep looking. I would rather not spend almost twice as much as I paid for the truck just to get an extra 150hp or so.

Ya I understand, it's a recreational use vehicle.

JohnnyBM931A2 · Sep 8, 2015

Bandit02 said:
Ya I understand, it's a recreational use vehicle.

Yeah.. If I was using the truck for profit like you I would be able to justify putting more income towards it. But since it is mostly just a toy for me I need to save money for more important things like maintenance.

74M35A2 · Sep 9, 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.

Yes, I'm 2 pages late. It is natural to want more and proceed that path. Keep in mind these trucks were designed and built via lowest bid contract to meet specific performance requirements, which they did. They were not built with the intent to be personally appealing as race cars after their disposal from the military. My personal opinion is opposite of yours, and that the 6CTA8.3 scoots my M925A2 along quite well, in completely stock form. It will be even more fun once turned up. I've heard the marine injectors for this engine likely have marine specific pistons (injection guidance), and simply putting the marine injectors into a non-marine engine will cause an increase in power, exhaust haze at idle, and cylinder wall washing.

I don't know much about the NHC-250 performance in these trucks, except that the fuel mileage is supposedly horrendous at 4mpg or so. Is there a chance maybe your engine is simply not in a good state of tune? People are adding a turbo to this engine because it is much easier and less costly than a complete engine replacement. OTR (Over The Road) trucks are rated to pull a minimum load of more than 40,000lbs, with up to a million mile warranty upon doing so, of which these trucks are not. I think it should be obvious as to why OTR trucks have more powerful, and more costly, power plants. I do agree with you though on what you'd like them to have, I would also greatly enjoy a 500hp ISX in my 9.

Audiophile31 · Sep 12, 2015

to those of you both turbo'd and working these trucks, how are your transmissions holding up with the added power and RPM?

jimk · Sep 12, 2015

WillWagner said:
<cut>Hey Bandit, can you tell me why Cummins went from that small, like tiny, cam to the big cam?

I read it was because they wanted a stiffer cam, better able to deal with higher pushrod loads (at higher HP and/or exhaust brake). The small journals limited the max diameter that'd pass thru the bearing...

I was amazed to read someone here is critical of adding a turbo to a naturally aspirated diesel. There are a lot of positives with few negs. I'd be more critical of a factory that sold an engine without one. Adding one is easy and doesn't cost much.

There are other ways to cool pistons though its unlikely it is even necessary on a low HP config. Turbos blow relatively cool air thru the chamber. Without additional fueling you have no additional heat. This additional cool air is basically inert (though it expands when heated so contributes to power production even though it doesn't burn (think- nitrogen side of a N2O set up). Extra air lowers EGT too. The more air the better. Cleans up the emissions and increase fuel economy. Boost on the intake stroke pushes pistons down too. That force creates a small amount of torque. That's free HP. Add some fuel and you get more. If you don't go wild you can get more hp combined with lower thermal stress than the naturally aspirated start point.

jimk · Sep 12, 2015

Audiophile31 said:
to those of you both turbo'd and working these trucks, how are your transmissions holding up with the added power and RPM?

The drive-train is not a weak link.

Bandit02 · Sep 12, 2015

jimk said:
I read it was because they wanted a stiffer cam, better able to deal with higher pushrod loads (at higher HP and/or exhaust brake). The small journals limited the max diameter that'd pass thru the bearing...

I was amazed to read someone here is critical of adding a turbo to a naturally aspirated diesel. There are a lot of positives with few negs. I'd be more critical of a factory that sold an engine without one. Adding one is easy and doesn't cost much.

There are other ways to cool pistons though its unlikely it is even necessary on a low HP config. Turbos blow relatively cool air thru the chamber. Without additional fueling you have no additional heat. This additional cool air is basically inert (though it expands when heated so contributes to power production even though it doesn't burn (think- nitrogen side of a N2O set up). Extra air lowers EGT too. The more air the better. Cleans up the emissions and increase fuel economy. Boost on the intake stroke pushes pistons down too. That force creates a small amount of torque. That's free HP. Add some fuel and you get more. If you don't go wild you can get more hp combined with lower thermal stress than the naturally aspirated start point.

I'm not critical. If someone spends time & money to put one I respect that. I just don't understand what you want to achieve. A cool whistle noise when your going to 7/11 to get a slushy?

Turbos don't blow cool air, unless the air has been substantively cooled through an intercooler. Sucking in and compressing air heats it up quite a bit. Thus you want a intercooler to thus "cool it down" the more cool dense air one packs into a cylinder the more power you'll get during the powerstroke. An example would be the cooler on the old Big Cam engines that are part of the intake manifold. The median in which air is cooled is engine coolant, so if that engine is warmed up lets say the coolest air is around 195* that being pressured into the cylinders....pretty warm. That not as efficient as today's intercoolers using the ram air effect.

I don't believe compressed air is enert. Exhaust gases are enert. They don't reburn. But compressed air with fresh oxygen will.

The heat of combustion is pretty intense. The aluminium pistons aren't cooled by the coolant flowing through the heads or block, the liners are cooled that way but the pistons are cooled by oil (thus, oil jets are needed). I'm sure the crank flings a bit up that way but surely not enough.

My belief in this theory is I had a customer come in with a 1973 Hayes COE tractor that was converted into a motorhome. It was armed with a NHC250. He put on jakes, had a Big Cam 2 oil cooler installed, he had the same exhaust manifold like in the 900 series trucks but what he did was made a custom flange to accept a turbo off a 290 (I think). It was put on right at the end beside cyl 5/6 inline. He did this because he ran a cab-over and couldn't put a traditional pulsed exhaust manifold on like on regular front nose trucks would accommodate. Also note he had no pyro/boost gauges for some reason.

Complaint was a heavy knock.

Took the last head off and discovered cyl 6 liner was scored and the wrist pin blue (from heat) and the piston wrist pin journals worn out. All he did was boot around the mountains in BC here on vacation a couple weeks a year. Not sure of what pump work he had done but as a recreational vehicle I wonder why he ran this set up. the valve guide seals where toast too, oil cooler was full of metal, the cam was scored but he didn't want it replaced so we let it go.

New liner, new piston, seals/gaskets/bearings, oil change, set the lashes, labor blah blah blah....$12500 bill. Have a nice day. No warranty, as it's modified horribly wrong. I did put a pyro on though.

I suppose if you run a turbo on a 250' and lightly use it will perform. If I do that and use it for lowbedding I'm quite sure it won't.

jimk · Sep 13, 2015

Bandit02 said:
I'm not critical...

I have no idea why guys spend their money turboing these engines...

But my 250' is 14 litres of crap...

Sound critical to me.

Turbos don't blow cool air, unless the air has been substantively cooled through an intercooler...

I said relatively cool air. At 18psi non-aftercooled air it is about 220*F. Under compression it goes over 800*F. Either of these are a lot cooler relative to the 3700*F combustion temps/ flame front. Air that is not supporting combustion is just along for the ride (and acts as a coolant of sorts, and as I said it will expand when heated).

I don't believe compressed air is enert...

I said basically inert. If there is no surplus fuel in the cylinder what is any additional oxygen going to react with?

The heat of combustion is pretty intense. The aluminium pistons aren't cooled by the coolant flowing through the heads or block...

Combustion temps only heat the pistons thru part of the power stroke. This is less than 180* of each 720* of crank rotation (the ex valve open early). Peak temp time is even shorter. After the fuel is injected and burned the cylinder vol gets bigger until the piston is at BDC. Pressure drops. Temps drop as gases expand. As soon as the ex valve opens press drops again. Cooler stuff comes in. These factors help keeping pistons from melting. Low HP engines like the 250 get by fine without oil nozzles. Same goes for hopped up 1000hp car engines

NHC 250 Turbo Conversion in M923

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