Add a turbo or get the 6cta 8.3l

6wdcummins83

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Hudson valley NY
I don't haul much, I don't tow I just like to drive around but I want more power. Should I add a turbo to my 925a1 nhc 250 Or should I go for broke and buy a takeout 8.3 and do some pump mods on the p7100 pump? I can't decide, the more I read the more uncertain I am. I know the issues I could run into with adding a turbo, I know about the lack of piston cooling oil squirters.
 

74M35A2

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Livonia, MI
The military 6CTA8.3 does not use a P7100 pump. It uses an MW pump, which pump section looks nearly the same (in-line configuration), and the fueling rate is adjusted in nearly the same manner.

If you want low end power, the NHC 250 is it, and start by changing the fuel button and add the dual fuel line mod. If you want to turbo it, there are a few threads here, read them thoroughly and then plot your path. It has been done successfully and at a reasonably low cost, despite the naysayers.

If you want more top end power and to double your fuel mileage, then the 8.3 is a better fit. You can further increase your top speed also with an 8.3L. A stock A2 (8.3L) 923/5 will do 67mph against the governor, of which can be further increased with an aftermarket set of governor springs. Be observant of your tire speed ratings though, this is your own decision and consider other drivers when doing so. 8.3L is rated up to 3400rpm and over 400hp in marine applications. You can not reach this power level with the pump/injector and intake configurations of the military version engine as-is though. Plan on $2500 for a used military 8.3L, not including shipping. I just drove my 925A2 to and from a local gathering last night, and I held 67mph for one hour straight on my 8.3L, it loved every minute of it and wanted more, but the governor pulls fuel out at 2150rpm. Will hit 2200-2250rpm on a downhill (68mph), but no more unless you tinker. Temp was rock solid at 185F and oil pressure 60psi. My 8.3L is at 1500rpm @ 50mph.

Hope that helps. If you want more of both (low and top end power increase), then neither engine will do it. Change to a used Cummins ISX, Series 60 Detroit, or another 500hp config. They can be had starting around $3500 and up, but they may also have the same top end RPM as the NHC250, leaving you with the same top speed as you have now, but much stronger acceleration.
 

wcuhillbilly

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421
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Devils Tower, WY
I jaked and Turbo'd mine, along with the fuel button and the dual fuel line,,,, for a step by step, look up "816 Jakes and Turbo" in the 5 ton hot rodding section...
It runs alot better and holds the hills better, but my achillies heel is still the lack of gears... but im driving a 36K lbs pig... your cargo body will be much lighter and nimble. The 14 ltr of the 250 is a simple and robust engine that is hard to screw up. the 8.3 ltr is a little over half of the cubes of the 250,,, and has no provision for a jake brake...,,, the 250 can be built into a great engine,, but most of the time finding the parts to turn it into a small cam 350 or 400 is a wash if a 350 or 400 is sitting in the local scrap yard...

Are you pondering the 12v conversion, are you thinking 10 spd trans, do you want A/C?????? if any of these are on the radar, I would suggest finding an older Mechanical E model Cat, or 60 series Detroit for a drive line swap... In the long run, you will be much happier with the bigger engine coupled to a trans that will allow you to expand to hydraulics in the future....
Side note.. with these drive line swaps, your front drive shaft will be no more. as the later will run a twin counter shaft trans and will fill the space in the frame rails where the front drive shaft is now...

Im up against this trans issue with my 816 right now... and have NO desire to go to the Allison...
 

red

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Eagle Mountain/Utah
You could rotate the tcase to make the front driveshaft clear a twin countershaft transmission. Only needs to go a few degrees.
 

74M35A2

Well-known member
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Livonia, MI
I would think using a non-twin countershaft trans would also fit? Not sure what that takes, I think maybe an old 7-speed or less? How are they doing it in todays diesel pickups? They are nearly 400hp now, and you can get a manual trans, and I promise it is not a twin counter unit. Could be another possibility....

I also have my pulse on this. I'd love to row gears rather than slush them, even though my Allison is calibrated perfectly and shifts like a Cadillac. Even on my current downshift, you could have an open top Coke from McDonald's on the floor full to the top, and zero would spill.
 

wcuhillbilly

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421
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Location
Devils Tower, WY
If a 7-8-9-10 speed single shaft would hold up it would be a dream... the Spicer 7 or 8speeds are junk, there are hundreds of testimonies out there and 3 locally here where medium duty trucks, rollbacks and small dump truck have smoked them. the last one I ran into tossed the 7 speed and found a 13 speed, and has been trying to shoehorn it in and hook up his hydraulics.
There is a rumor that Spicer made a 10speed single shaft, I have never found one, I am willing to look into it if one ever comes along... 2nd problem is finding parts for an old,,, really old spicer, as when they pop, they tend to take out the rear of the housing.
Basically the 7-8speed spicers that would bolt up to our SAE 2 bell patterns wont hold up to our driveline torque or the weight of our rigs reverse delivered from the wheels back to the engine... the 855 cummins will take the abuse, the rockwells and the Rockwell T case will take the abuse but the 7-8 speed trans will pop the rear of the trans. Modern 6 speeds like the G56 are really weak compared to the Spicer 5spds, not to mention they are about 1/3 of the size, We had trouble with the 6spds in dodges, with the 5.9, I shutter to think what an 855 will do to one if, you could find the parts to hook it up.

Some have clocked their T case, but I ponder that as the mounting points would then be stressing one side at an angle more so than the other, which will ultimatly lead to some sort of driveline problem. THis is a nice way to clear the front drive shaft around the new trans, but then comes the angle going into the front axle,,,, The driveline with as many U-joints as it has, is not near as forgiving to misalignment as your pickup truck,,, only thing is with a 5 ton, its harder to find the problem untill it really shows itself with a major hit to the checkbook...

For a cargo box running around empty, as basically a pavement princess, the 7-8 speed spicers would work,,, but for any of us who actually use our trucks,,,,, they are not worth the time much less the money to install. Failure will be the final outcome..
 

red

Active member
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38
Location
Eagle Mountain/Utah
I would think using a non-twin countershaft trans would also fit? Not sure what that takes, I think maybe an old 7-speed or less? How are they doing it in todays diesel pickups? They are nearly 400hp now, and you can get a manual trans, and I promise it is not a twin counter unit. Could be another possibility....

I also have my pulse on this. I'd love to row gears rather than slush them, even though my Allison is calibrated perfectly and shifts like a Cadillac. Even on my current downshift, you could have an open top Coke from McDonald's on the floor full to the top, and zero would spill.
The transmissions used by 1 tons have a much lower duty rating at those power levels. The Spicer 3053a from the deuce has a heavier duty rating than the NV4500 for example. If you don't drive the truck often its fine. If you haul regularly or have a heavy truck (wrecker) a medium or heavy duty transmission is required.

A straight 6 or 7 speed will work. Same overdrive ratio with a little bit smaller Gap between the gears. The larger twin counter shaft transmissions are heavy duty with more gear choices, and certain models have better overdrive ratios.
 

6wdcummins83

Member
41
3
8
Location
Hudson valley NY
To those who have done the turbo, what side outlet is the HT3B is it a 5" down pipe? I'm just impatient to wait for the turbo to get here in a week to get the dimensions And order the exhaust tubing. I'm doing a 5" straight pipe I think I have all the parts in my "cart". I was just unsure about the outlet diameter of the turbo exhaust. I promise plenty of pics and vids.
 

wcuhillbilly

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421
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Location
Devils Tower, WY
To those who have done the turbo, what side outlet is the HT3B is it a 5" down pipe? I'm just impatient to wait for the turbo to get here in a week to get the dimensions And order the exhaust tubing. I'm doing a 5" straight pipe I think I have all the parts in my "cart". I was just unsure about the outlet diameter of the turbo exhaust. I promise plenty of pics and vids.
My 4LHR Schwitzer was a 5", I just used a standard flange from NAPA truck with the coordinating band, this gave me about 6" to weld my 90* onto to start the downward migration to my old 4" pipe. 2) 90*s a Flange, and a short coupler with a reducer had me where I needed to be. Then welded it and put a couple band type clamps on.. Works fine,,, just make sure you put a load bearing hanger outside, so that the turbo isnt supporting the weight of the stack.
 

jarhead1086

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112
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Location
Farr West, UT
I ran 5" all the way. Standard flange welded to a 45 to a chunk of straight to a 90 all welded in one. I isolated with a section of triple wall stainless flex pipe to connect to the straight run out the back. Motor and the straight run can move independent without loading each other like hillbilly said. They are fully supported. I think it sounds great with a very low restriction stainless mbrp muffler.
 

jarhead1086

Member
112
1
16
Location
Farr West, UT
I ran the fat return line to a port in the block right below turbo. Just remove threaded plug. The smaller pressure line went where the oil sample valve was. There are pictures on ss. I'm out of state on my phone right now.
 

wcuhillbilly

Member
421
2
18
Location
Devils Tower, WY
The oil supply to the Turbo can be gained by removing one of the 1/8 plugs on the oil cooler, above generator is a larg round cast housing with coolant lines running into it. remove one of the pipe plugs and (make sure there is oil.... if water/oil you have big problems) Thread a 1/8 to 06JIC fitting in and run your AN line to the supply of the turbo... pretty simple really,,, Turbo drain,,, run a big line as its a gravity drain, Like Jarhead1086 said, there is a 3/4 pipe plug on the block, just insert your 1/2 ratchet and twist. Insert nipple fitting of your choice (I was lucky enough to scavenge this from my donor engine) and away we went.
 

wrenchturner6238

Member
Steel Soldiers Supporter
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18
18
Location
Liberal Kansas
I have not seen shim part numbers on here but I have seen the (plunger) Button part numbers.[h=2]
Increasing PT pressure[/h]Line #18 is where the button numbers are
 
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