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NHC 250 Turbo Conversion in M923

Bandit02

Bandit02

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jimk said:
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
Click to expand...
I'm 100% critical of my engine, I rely on it for as a additional source of income.

All air forced into a cylinder during the intake stroke is supporting combustion - it's compression ignition (Lots of air, small injection). Anything not "burnt" is wasted energy, just hp going out the tailpipe or turned into heat. I believe on gas engines there alot of excess air during combustion, hence why they use 02 sensors in their emission systems. And the lack of air during combustion will create a smokey/sooting situation and more particle matter and more heat.

Basically, your saying one installs a turbo but does not need changing the fuelling parameters (No additional fuel no additional heat). You would have a lagging engine.

If combustion temps only heated the piston through part of the powerstroke there wouldn't be a need for oil jets on heavy truck engines (my 2013 Ram 6.7 Cummins has them as well). Aluminium has a low melting point so keeping them cool is the utmost importance, and oil absorbs heat very very well, if I had steel pistons in my 250' I would turbo it and roll the dice.

Your right though, low HP engines like the 250 get by without oil nozzles...stock. If you throw a turbo on I imagine it's because you want more power = go faster/tow more? Add more air, your going to need more fuel, generate more heat, and that heat needs to be dissipated somehow to atmosphere.
 
jimk

jimk

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Right...

Moving right along, folks considering this mod may recall how engineers made the LD465 into the LDT465. They had no problems (except for a head gasket that didn't cut it on the nat aspirated LD). There was also a bolt on upgrade called a clean air kit. Lots of them are around. Reliable, even when turned up to silly levels. Remarkable, considering the high 22:1 C/R

There was post in the other thread, just a cut and paste text, about the Cummins 'Smoke Kit' for the 250. Not much detail. What I found interesting was the company offered it. They probably still have details somewhere. I'd be interesting to know what changes they specified. Finding it might require a pal at the parts counter.

http://www.steelsoldiers.com/showth...turbo-and-pics&p=890723&viewfull=1#post890723
 
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162tcat

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No reason to continue debating this with every person who posts on here. Many people on ss, myself included, have had great results by adding a turbo and bumping up the power. It's your truck, do what you want and feel free to share pictures and your results after you do your engine swap.
 
jarhead1086

jarhead1086

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Exactly what 162cat said. I am at higher elevation and the turbo helped greatly. It holds hills better, sounds better, and the EGT's dropped 300 F. Cost is the only downside I have found and I don't drive these to save money. I drive them to feel like a young Marine again and have fun. This old girl has a plush retirement parked in my garage and will never have to work hard again. As many miles as I drive it will last many years. I appreciate all those that encouraged me to convert it over.
 
74M35A2

74M35A2

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jarhead1086 said:
Exactly what 162cat said. I am at higher elevation and the turbo helped greatly. It holds hills better, sounds better, and the EGT's dropped 300 F. Cost is the only downside I have found and I don't drive these to save money. I drive them to feel like a young Marine again and have fun. This old girl has a plush retirement parked in my garage and will never have to work hard again. As many miles as I drive it will last many years. I appreciate all those that encouraged me to convert it over.
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That's good enough reason right there! Anything with a spooling turbo sounds like it is going to rip the guts out of whatever it is hooked to. 300F is a fabulous drop, that sounds like in increase in reliability to me... It will help to prevent this (advance to 2:03 for the fabulously funny part):

https://www.youtube.com/watch?v=gwNfhEUqfuY
 
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74M35A2

74M35A2

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Pop-Rocks in the fuel tank provides for some good entertainment. Love the You Tube commenter that said "That was knarly, do it again!".
 
6

6wdcummins83

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Hudson valley NY
So I'm about to collect the parts to add a HT3B turbo to my m925's 855. Only to clear up the smoke (wasted unburnt fuel) and hear a little bit of spool. I'm not really looking to add tons of power. It's not gonna be hauling or towing alot, I'm running 53's as well. its a drive around show off truck with a little bit of off roading mixed in. I'm not trying to make a 400 hp engine, maybe 270-290, will I be safe??
 
1

162tcat

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Any manifold will flow plenty for that setup. I'd look for one without the after cooler to simply things. Any of the older 335 cummins should have what you need.
 
M2Guy

M2Guy

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Canton, Ohio
Of you guys that have done the turbo conversion, fuel button replacement, and shimming, what horsepower range to you think you are in and how is your Allison MT654 holding up? As you all know they are rated for 300hp and 950ftlbs of torque.
 
jimk

jimk

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M2Guy said:
Of you guys that have done the turbo conversion, fuel button replacement, and shimming, what horsepower range to you think you are in...cut
Click to expand...
From link above, post 102-

"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....

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..."



so for a 240 HP motor maybe 30HP, perhaps a bit more if you go under #20
 
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