: 6BT Into 5-Ton Military Truck - Brainstorming



SixSpeed
04-24-2010, 04:10 PM
(Note: W00t, I got 10 random posts, so now I can post this thread! It wouldn't let me before since it "contained links or images"...which is doesn't. OH WELL!)

Hey Guys,

I am pretty sure I would like to go ahead and get this project rolling. I have an M817

5-Ton Military truck, which I would like to re-power with a 12V 6BT.

The truck is "bobbed" (rear axle remove/truck shortened w/ cargo bed) - Weight ~

15,000lbs. It is currently powered by a NHC-250 Cummins. N/A 855 cu.in and 240hp/658ft.lbs.

My reasons for the swap:

1.) Power - the 6BT can easily make more power than the 250 which is currently in

the truck. I would be shooting for around 300hp out of the 6BT, which can be done quite

reliably.

2.) Reliability - I know the NHC-250 in the truck isn't unreliable by any means,

but if you turn up the fuel at all, which I know I would be helpless to avoid, you can run

into heat issues. The 250's have no piston cooling. The 6BT would have an easy life in this

truck. Maybe 2000 miles per year?

3.) Fuel Economy - Current fuel economy....maybe 7 MPG? I know my buddies Dodge

3500 (Dually/4x4/Quad Cab) towing ~8000lbs (Putting the weight of that combo a couple

thousand pounds over what my truck would weigh. It still manages 17mpg towing. I don't see

why I couldn't acheive at least 15MPG, any opinions?

4.) Weight - The 6BT is MUCH lighter than the 250 in the truck. I could drop over

1000lbs out of the front end with this swap. This would bright the weight of the truck to

14,000lbs. The weight of a 1-Ton truck towing a light/medium load.

5.) Speed - This might sound silly with this truck, but I can get a little more

MPH out of a 6BT. Currently @ 55MPH I am turning 1700-1800RPM (Redline on the 250 is ~

2100). It would be really nice to be able to cruise @ 60MPH, which would yield 2000 RPM,

which the 6BT shouldn't mind at all. Keep in mind this truck sees limited highway time.

Maybe 1000-1500 highway miles per year.

What would be required:

1.) I would need to find an SAE #2 bellhousing adapter. Can these be found for sale

easily? I know they make them.

2.) I would have to work out the flywheel/clutch adaptation issues as they come I

believe, but this isn't really a concern to me. I have access to machining services.

3.) Motor mounts - Easy

4.) Oil pan/front axle clearance? I don't think this will be an issue, but I need to look

into it a little more.

5.) Starter - I guess it depends on the bell housing, but anyone have any thoughts about

using the 24V Starter from the old setup?

6.) I need to find a power steering pump (going to assume a PS pump from a 1-Ton won't be

up to the job?)

7.) I also need to find a good air compressor to run with the 6BT.

6.) Would have to fab mounts for the 24V Generator - Easy...


I think that's all that is running through my head right now. Thoughts/opinions/sugestions?

THANKS!!

BobS
04-24-2010, 05:16 PM
If it was mine I would seriously start looking for a 6CT Cummins. There are a lot of them in wrecking yards that specialize in tractor trailer size trucks. There may already be 6CT's that have the correct size SAE housings that may be close to being a bolt in deal. I'm not that familiar with them to go into the finer details. The down size to using a B series Cummins is you have already stated that you have the temptation for turning up the injection system. In this case the gain could become zero because of increased fuel consumption from turning up the injection system.

There were some IH trucks that were just beyond the medium duty chassis in the 28,000 GVW rating that used Cummins 24 valve B series engines. These can sometimes be had at cheap prices. I saw 2 locally that were used as bottled gas delivery trucks that sold complete & in driving condition in the $3,000 price range. That may be the best source of all of the parts in one shot.

SixSpeed
04-24-2010, 05:20 PM
Thanks for the input.

I was considering the 6CT series, but I just don't know enough about those engines. Haven't been able to find what I needed to know, that is why I leaned towards the B series.

Power?
"Tuneability"?
Fuel Economy?
Reliability?

EDIT: Few other things I just thought of. Redline? And the cost of 6CTA's seems to be much more than 6BT's.

lskinner4
04-28-2010, 05:47 PM
Have you visted/know about the steel soldiers forum? Just google steel soldiers and its first on the list. It is this type of forum but is for Military Vehicles and alot of passionate MV owners with alot of good info

SixSpeed
04-28-2010, 05:52 PM
Yep, I am an avid SS member, I just figured I would get some opinions over here as well :)

tndonor
04-30-2010, 09:10 AM
I have read of a duece with a 6B and the owner liked it.

The questions I had for this type of swap (I have contemplated a 6C duece swap for awhile) are still unanwsered. The 250 Cumminsmakes almost 700 torque out of the gate. But it has MUCH more rotating mass to handle a load (hills, offroad, trailering, etc). The Cummins 6B will make those power level easy yes but has a far less rotating mass to cushion the load so to say.

In the movie tokyo drift, the import cars got small blocks for the driving scenes.....because the engines couldnt handle the load of drifting uphill, etc. These motors can make 500 hp plus but compared to their torque curve, it is small and they have a small rotating mass.

I could be way off base but that is the thought I had on this issue

chevy43
05-07-2010, 12:12 AM
I wouldn't do it. The 250 can be made to make 300 pretty easily with a turbo and more if you stuff an air to air intercooler in the front with a little grill modification. No piston coolers just means you have to be more carefull with EGT. You can get real Jakes for it pretty cheap too. Also You can install a 9 to 13 speed in there pretty easy too and then really use the cummins in the sweet spot. I'd guess you would get about 9 MPG instead of 6 MPG with the 6BT. I doubt you would ever recover the time and energy of the swap in fuel savings. You could also take off the engine driven fan and use an electric and save some milage running the big fan. Another thing to do is mill out some extra drive flanges and lock out your sprag unit with an air vavle so you aren't turning the front axle on the road.
We put a set of super single Hemet wheels and tires on one and that gives you 65MPH if you want to go that fast.
One more thing is that the natral aspriated NH250 just sounds great!
On an 800 series who really cares about the extra weight anyway? You wouldn't drive that if you cared about weight...
The 6BT would look silly in that giant engine compartment.
The NH 250 makes about 600 lbft from 500 rpm up. It's nice to have 855 cubes for bottom end torqe.

SixSpeed
05-07-2010, 12:16 AM
I wouldn't do it. The 250 can be made to make 300 pretty easily with a turbo and more if you stuff an air to air intercooler in the front with a little grill modification. No piston coolers just means you have to be more carefull with EGT. You can get real Jakes for it pretty cheap too. Also You can install a 9 to 13 speed in there pretty easy too and then really use the cummins in the sweet spot. I'd guess you would get about 9 MPG instead of 6 MPG with the 6BT. I doubt you would ever recover the time and energy of the swap in fuel savings. You could also take off the engine driven fan and use an electric and save some milage running the big fan. Another thing to do is mill out some extra drive flanges and lock out your sprag unit with an air vavle so you aren't turning the front axle on the road.
We put a set of super single Hemet wheels and tires on one and that gives you 65MPH if you want to go that fast.
One more thing is that the natral aspriated NH250 just sounds great!
On an 800 series who really cares about the extra weight anyway? You wouldn't drive that if you cared about weight...
The 6BT would look silly in that giant engine compartment.
The NH 250 makes about 600 lbft from 500 rpm up. It's nice to have 855 cubes for bottom end torqe.

Why do you think a 6BT in this truck would get such poor fuel economy? The 6BT was originally designed for medium duty truck applications, which is what this is.

chevy43
05-07-2010, 10:43 AM
I would call the 800 series a heavy duty truck. They weigh in the neighborhood of 18k empty and are as big and heavier than most over the road big rig tractors.

The 6BT does about .35 - 36 LBS of fuel per HP HR and the NH250 does about .38 - .4 per HP HR. The NH250 is a good efficient engine.

The 800 series probably needs about 100 hp or more to cruise at 55 mph. It has bad aerodynamics, 10 bias ply tires and 3 axles and gears etc spinning all the time.

100 HP x .35 lbs per HP HR = 35 lbs fuel per hour. Thats about 5 gal per hour. (Diesel weighs about 7 lbs per gal.) 55 miles /5 gals = 11 MPG (best case). It's a big heavy truck with a lot going on and it takes more power and fuel to move it than and = equally loaded Dodge truck pulling a trailer.
The NH250 will run forever at full throttle with no EGT issues. The 5.9 will be working hard to do what the NH250 will do relaxed.
And I still think the 5.9 would just look ridiculous in there. The other thing that comes to mind is "dont fix it if it aint broke".

nhdiesel
05-07-2010, 04:56 PM
Sixspeed, You are hoping for the reliability, mileage, and power of a medium duty road truck. But those trucks are much more efficient than the truck you want to put the engine in. You have a transfer case spinning, inefficient axles and poor gearing for road use, and aggressive tires that lower the mileage. The aerodynamics of the road trucks are much better. Even the comparison of your friend's Dodge with a load doesn't work, for the same reasons. Its much more efficient putting the power through a NV4500 with overdrive, a NP441HD t-case, and a Dana 80 rear axle is much more efficient than putting it through a large Spicer transmission, 5-ton t-case, and 5-ton axles.

My guess is that after the swap, you might hope for 10mpg if you are lucky.

Now lets weed out a few of your requirements for the swap-

Power- Add a turbo to your 250 Cummins and you'll have all the power you want. Or install a 400 Cummins, which fits right in, and REALLY have power. You'll go through the 5.9 swap, tune the 5.9, and just barely get the power output of your 250. If you want more power, it starts costing, and you end up cheaper working with what you have or swapping in a larger Cummins. In fact, another engine to consider would be the 8.3 Cummins, which is similar to the 5.9 but larger internally.

Reliability- At 2k miles a year, reliability doesn't seem to be a factor. Any diesel motor would last as long as you'll be driving the truck, so you don't need a 5.9 for that. Those 250 Cummins engines are extremely reliable, which is why they were one of the most common large diesels ever used.

Fuel Economy- At 2k miles a year, why is it a concern? You will spend FAR more doing a swap than you will EVER save. When I did my Durango 4bt swap, I did it very cheaply, got an improvement of 15mpg, and its my daily driver- and I still figured it would take nearly 2 years to pay for itself, and that included adding in cost of tuneups I would be saving.

Speed- Your money would be better spent swapping transmissions. Go with a 9 or 13-speed OD transmission, and you'll gain top speed and you'll have more power for pulling (more gear options).

Jim

powerhouseduece
05-07-2010, 11:33 PM
I have thought about the swap as well if I ever bobbed my m818. Your better off looking for a complete 6cta out of a m900a2 series or you can save time and money by just looking for a 400 big cam. Thats what im looking at doing after I do the 4bt swap in my silverado. Keep a eye out for tractor scrap yards, I let 3 400BC's slip through my fingers and regret every second. I was planning on running my stock 5 speed if I bobbed it, the motor should have enough balls to defeat the evil 3rd to 4th gear shift. Since im planning on keeping it 6x6 im ont the hunt for a 400 and a 10spd tougher to to make the swap simpler. Hope this helps.

pyrojoe22
03-02-2017, 07:46 PM
And now that the M939's have flooded the market, this question comes up again. I own multiple of both 855 N/A Cummins and 8.3 Turbo Cummins 5-Tons (M923, 925, 934). The 855 is a turd. Comparing the 855 on 43" tires to the 8.3 on 49" tires, the 8.3 runs circles around the 855. Put the 855 on 49's and it can barely go 30mph. Put the 8.3 on 43's and it feels like a hot rod. Both are roughly 250hp motors (8.3 is actually 240). I have a very large grade by my house that I use to compare everything. My 855 on 43's unloaded struggles to maintain 45mph. My 8.3 on 49's keeps 55mph loaded. Obviously a 400 Cummins would be the end-all solution, but that's expensive, the turbo is hard to fit, and there's not a lot of real estate for the intercooler. The 8.3 is my preferred motor, even though it has an MW pump instead of a P style pump.

For trucks that came with the 855, I am currently debating whether to throw money at them in the form of charged induction with risk of blowing the motor up (which many have done just in stock form since they pretty much sat for the last 15 years). Or throw in a 12 valve with a P7100. Question is, would I go with a very cheap 160hp P7100 or the elusive 215hp? Cost is a big thing here. I picked up all my 5 tons for less than $2300. My 855's were $1300 each, so I basically have $1000 to spend on them, plus whatever I get for selling parts, to get them to the level of the 8.3's that cost $2300. I can sell a good 855 for $1000 now easily since there is now demand, giving me $2000 for a 12 valve with cheap mods. Or I can spend $1000 on a turbo and manifolds for the 855. Seems to me that my 8.3's were much better investments; they're as strong as I need and didn't require me to lift a hand to build them how I want; not to mention cheaper power in the end.

I'm very curious if SixSpeed ever did the swap?! I too think it's dumb to even remotely think about mileage. If mileage is a concern, then you can't afford to drive these things. For a simple comparison, I've tracked a couple and have seen 11mpg with the 8.3 on 49's average 65 mph over 3 hours, and 9mpg with the 855 on 43's on the same trip back from base. The 8.3 wins again! I know people have thrown out the argument on multiple threads about the 855's inertia over the 5.9 and 8.3, but guess what? I've actually been using mine for work (not play), to haul heavy equipment, hay, water, trees, etc., and the 8.3 outperforms the 855 on almost every front. I don't notice that inertia going up a hill with the 855, and that's where it should shine. You can't hold the idle up on the 855 because it tries to run away, whereas the 8.3 will sit wherever you set it. The 8.3 is 90 times easier to start in the cold.

To conclude my thoughts, it is clear from my experience over the last 1-1/2 years of operating these 4 rigs that the 8.3 is superior to the N/A 855. To decide if the 5.9 would be adequate, you simply have to compare the 5.9 to the 8.3. How do the peak torque's and torque curves compare? It won't take that much to get a 12 valve up to the same point as an 8.3. We're not going for 600hp. We're trying to match 240hp and add a little bit more torque than the 8.3. The 855 made 250hp/685 lb*ft. The 8.3 made less hp, but we don't care about hp, we care about torque. The 8.3 made 240hp/745 lb*ft. The 855 has 68.6% more displacement and thus they gave the 8.3 roughly 9% more torque to compensate. Doing a ratio of displacement vs. torque increase and applying same ratio to the 5.9 vs. 855 says we need 808 lb*ft. Interpolating simply between displacement and torque for the 3 engines says we need 770 lb*ft. So we're within 5% and I would err on the high side. So in theory, if you're going to run a 5.9, I'd shoot for at least 810 lb*ft and maybe don't be afraid to go with 900 or 1000 if it's easily doable. In my case, I have 2 855's that either need to learn how to move, or I'm going to sell the trucks. So I think I'll start by turboing 1 and 5.9 swapping the other and seeing which result I like better.

Dougal
03-03-2017, 01:25 AM
The only things a smaller engine will produce in a truck like that is lower noise and slightly better fuel economy.

Sounds like your 855 is sick PyroJoe. While you'll expect a big difference in how a turbo vs NA engine drives; torque curves etc; with similar rated power they should be able to move the same trucks up the same hill at the same speed. If one can't then it's not producing rated power.

Add a turbo and 10psi to any old diesel engine and it'll warm up faster, burn cleaner, run more efficiently and be quieter. It's also a whole lot easier to do than an engine swap and if tuned correctly give you about 40% more power with cooler EGT.

For a non turbo engine don't go more than 10psi, don't advance the timing and don't run EGT over about 1200F.

pyrojoe22
03-03-2017, 08:12 AM
I've owned a half-dozen 855's and still own 2. I doubt all 6 were sick. They've ranged from 1000 miles to 50k miles. 1 was definitely sick. The other 5 were all the same, though. Google the 855 vs 8.3, and you'll see everyone shares this opinion.

Again, this isn't about mileage. If you care about mileage, then you can't afford to be driving a 5 ton. This is about power and not impeding traffic. The challenging part is finding a dyno close by that will handle one of these things. I've already removed the rear drive shaft on one so I can put it on a RWD dyno, but I'll probably have to go to a big city to use a semi-tractor dyno because of the size of these things. I want to dyno the 855 and 8.3 in stock form, then dyno the turbo NHC 855 and 5.9 swap. It would also be nice to dyno the 855 with the bigger fuel buttons and dual fuel line mods. My M934 van is what I'm going to be messing with first. I'm building it into an overland camper to take to the off road park and live out of for a week when I go on vacation. I at least need to be able to maintain the speed limit on that 4 hour drive. This thread is 7 years old, so I won't be too worried about taking my time to post back my results. But I fully intend to 5.9 swap one 855, and turbo the other. At least then people can have some actual real-world-data to go by instead of peoples' opinions that have never done the swap.

I think everyone needs to go watch an episode of Diesel Brothers and pay attention to the details of one of their builds. They throw Duramax's and 5.9 Cummins into trucks rolling on bigger tires than these (53") all the time and use light duty truck transmissions.

Dougal
03-04-2017, 11:41 PM
Dyno sure will put the BS to rest. Please post up the results if you can make it happen.

If you build for TV it only has to last one episode. But I've never seen diesel brothers.

pyrojoe22
03-05-2017, 08:44 AM
Don't worry, I'm dead serious about this project. So serious in fact, that yesterday I went out and bought a 1994 12 valve Dodge 2wd with 102k miles on it! Going to be my daily driver for the next year while I get the motor tuned to where I want it and get the kinks worked out of it, then it will be going into one of my 939 series trucks.

RXT
03-14-2017, 07:03 AM
…..I own multiple of both 855 N/A Cummins and 8.3 Turbo Cummins 5-Tons (M923, 925, 934). The 855 is a turd. Comparing the 855 on 43" tires to the 8.3 on 49" tires, the 8.3 runs circles around the 855. Put the 855 on 49's and it can barely go 30mph. Put the 8.3 on 43's and it feels like a hot rod.


Both are roughly 250hp motors (8.3 is actually 240).

The reason the 855 is a turd…it doesn't have a turbo. Unlike a gasser, diesels really need a turbo or a supercharger to breathe. Without forced induction, the only way an N/A diesel can breathe is by rpm, but unlike gassers, a diesel doesn't rev very high, so they will always present with limited breathing capability. Yes, some N/A diesels can put out similar HP & TQ figures as a turbo diesel, but because of the limits in breathing, the N/A diesel is going to perform differently. Take your example of going uphill. As an N/A diesel pulls and begins to face resistance, the rpms begin to drop. As the engine loses rpm, it loses the air it needs to make power. It's like a 30yr chain smoker with emphysema trying to run a marathon. Turbocharging a diesel was the game changer. With a turbo, the diesel no longer needs to depend on rpms to breathe. So in the uphill battle, the turbo can keep delivering needed air to the engine so it can continue to make power which helps keep the load moving and the rpms up.



For trucks that came with the 855, I am currently debating whether to throw money at them in the form of charged induction with risk of blowing the motor up (which many have done just in stock form since they pretty much sat for the last 15 years).

The engine won't blow simply because it sat. As for turbocharging an 855? The 855s were often equipped with turbos when used in over-the-road trucks. Of course it will depend on what you've got to work with. Many later 855s were the "Big Cam" version. I would suspect that the 855s used in military vehicles were purposely spec'ed without the turbo to save money and prolong the service life of the engine, especially when you consider these trucks would be piloted by 18 yr olds with no real driving or mechanical experience.

The advantage of turbocharging the 855 is, cost. The engine is already there under the hood and it's already bolted up to your transmission. It will have some other advantages. It might not make as much HP, but it will definitely make much more torque due to it's larger displacement and longer stroke.


Or throw in a 12 valve with a P7100. Question is, would I go with a very cheap 160hp P7100 or the elusive 215hp? Cost is a big thing here. I picked up all my 5 tons for less than $2300. My 855's were $1300 each, so I basically have $1000 to spend on them, plus whatever I get for selling parts, to get them to the level of the 8.3's that cost $2300. I can sell a good 855 for $1000 now easily since there is now demand, giving me $2000 for a 12 valve with cheap mods. Or I can spend $1000 on a turbo and manifolds for the 855. Seems to me that my 8.3's were much better investments; they're as strong as I need and didn't require me to lift a hand to build them how I want; not to mention cheaper power in the end.

The advantage of the 6BT is tons of support and dozens of ways to make power. It will all depend on the size of your wallet


I'm very curious if SixSpeed ever did the swap?! I too think it's dumb to even remotely think about mileage. If mileage is a concern, then you can't afford to drive these things. For a simple comparison, I've tracked a couple and have seen 11mpg with the 8.3 on 49's average 65 mph over 3 hours, and 9mpg with the 855 on 43's on the same trip back from base. The 8.3 wins again! I know people have thrown out the argument on multiple threads about the 855's inertia over the 5.9 and 8.3, but guess what? I've actually been using mine for work (not play), to haul heavy equipment, hay, water, trees, etc., and the 8.3 outperforms the 855 on almost every front. I don't notice that inertia going up a hill with the 855, and that's where it should shine. You can't hold the idle up on the 855 because it tries to run away, whereas the 8.3 will sit wherever you set it. The 8.3 is 90 times easier to start in the cold.

The simple fact is, diesels really need a turbo, and the turbo gives these things power, fuel economy, and makes life easier. Inertia is nothing without power to back it up


To decide if the 5.9 would be adequate, you simply have to compare the 5.9 to the 8.3. How do the peak torque's and torque curves compare? It won't take that much to get a 12 valve up to the same point as an 8.3. We're not going for 600hp. We're trying to match 240hp and add a little bit more torque than the 8.3. The 855 made 250hp/685 lb*ft. The 8.3 made less hp, but we don't care about hp, we care about torque. The 8.3 made 240hp/745 lb*ft. The 855 has 68.6% more displacement and thus they gave the 8.3 roughly 9% more torque to compensate. Doing a ratio of displacement vs. torque increase and applying same ratio to the 5.9 vs. 855 says we need 808 lb*ft. Interpolating simply between displacement and torque for the 3 engines says we need 770 lb*ft. So we're within 5% and I would err on the high side. So in theory, if you're going to run a 5.9, I'd shoot for at least 810 lb*ft and maybe don't be afraid to go with 900 or 1000 if it's easily doable. In my case, I have 2 855's that either need to learn how to move, or I'm going to sell the trucks. So I think I'll start by turboing 1 and 5.9 swapping the other and seeing which result I like better.

Allow me to explain something a little off the topic (but would still apply as a response). There is a distinct relationship between HP and TQ, but not to be forgotten we need to include RPM. All engines produce HP, and HP is derived from the mathematical formula;
HP x TQ / 5252
The number 5252 is an interesting part of the formula, as it happens to be the exact rpm which all engines produce equal amounts of HP and TQ. Factoring in the importance of RPMs, the formula bears out that any RPM above 5252 rpm, an engine will tend to produce more HP than TQ. Any RPM below 5252 rpm and an engine will tend to produce more TQ than HP. Most diesels operate well below 5252 rpms, so they will always tend to produce much more torque than horsepower. Thats not to say that HP in a diesel isn't important, but knowing the dynamics and relationship between HP and TQ gives us greater insight. When we look at power in a gas engine, we simply read how much HP it makes. We say 600HP, thats a lot! But, that level of HP in a gas engine doesn't tell us anything about the "grunt" behind it. Assuming that this "600HP" was produced above 5252 rpm, we can conclude that this engine isn't producing 600ft-lbs. We may not know the exact amount without measuring the torque on a dyno, but we do know the dynamics of the formula. The same applies for the diesel. At 600HP, the diesel is producing more than 600ft-lbs, probably a lot more. This is why a 600hp gas engine can't pull the loads that a 600hp diesel can.

Based on displacement and RPM, the 5.9 Cummins typically produces two ft-lbs of torque to every horsepower it makes. So if you have the 160HP version, it should make at least 320ft-lb (Actual is 400ft-lb) The opposite would also be true. To reach 800ft-lb, you would want a 5.9 capable of about 400HP. Different engines will have different "ratios" The "855" is 2.4 times the size of the 5.9 6BT, which gives it almost 3ft-lbs of torque to every horsepower it makes. And the 855 would probably do it with less RPM. The 5.9 will be adequate, but it would need to be turned up and spin a few more rpms. This of course will add a little more stress and increased wear. In it's favor, you can push the 6BT much more than the 855. The 8.3 OTOH is basically a larger version of the 6BT, and will be easy to turn up a lot if you want.

Ed

pyrojoe22
03-14-2017, 08:23 AM
Ed, Thank you for the reply. Although I'm not really sure you've said anything that hasn't already been said before, either in this thread or on steelsoldiers, they are good points nonetheless. In short, you basically just said you would also like to see a shoot-out between a turbo'd NHC-250 855 and a turned-up 5.9. And I intend to give that.

Currently working on a compound turbo setup for the 5.9. I can already tell that this motor is going to be awesome. A way better candidate than the LBZ Duramax I was planning on swapping in. Lots more low-end torque.

One important thing you forgot to mention is that the NA 855 doesn't have piston oil-squirters and really wasn't designed for a turbo. Other than the coincidental displacement, this motor is really nothing like the Big Cam 400 motors. But by golly, I'm gonna throw some boost at her anyway and see what she'll put out. I won't be pushing much more than 10-15 psi with this old girl.

Not sure if you're saying you don't believe me that a bunch of these military 855's have blown up 30 miles or less out of the IronPlanet gate, but they have. I've seen it. It might not be on YouTube, but it happened.

With your HP vs. TQ formula, don't forget that HP is just a measurement of HP at a given RPM, but don't confuse that and think that you can find your max HP from your max TQ. You can find your HP at your max TQ RPM, but your MAX HP is going to be at an altogether different RPM where the TQ is lower (generally speaking). People seem to really struggle with this concept.

RXT
03-14-2017, 10:18 AM
Ed, Thank you for the reply. Although I'm not really sure you've said anything that hasn't already been said before, either in this thread or on steelsoldiers, they are good points nonetheless. In short, you basically just said you would also like to see a shoot-out between a turbo'd NHC-250 855 and a turned-up 5.9. And I intend to give that.

Not sure if it was said anywhere else, as I hadn't read it…Not saying I don't believe you, just saying I hadn't read it anywhere else…. I wasn't really saying or implying that I'd like to see a shoot out, but I wouldn't be against seeing it. At the least it would either validate what I would predict or completely invalidate what I would expect, so bring it on….Love to see it



One important thing you forgot to mention is that the NA 855 doesn't have piston oil-squirters and really wasn't designed for a turbo.

The 855 was offered in a few different configurations including a turbo version. What I don't know is which version you have. I don't think the turbo version had piston squirters either and I believe they were safe because they didn't produce much boost. The squirters were introduced to help cool the pistons on high output diesels and is a relatively recent innovation. I would only be concerned with nuking pistons if you were pushing high boost and injecting a ton more fuel. This would create high EGT under a lot of engine load and could melt pistons even with squirters. You can certainly implement methods to help reduce EGT, such as installing an intercooler and maybe introducing water injection, to help further cool the charge air going into the engine. But most of all don't go for big boost on these without a ton of durability mods (and yes, it's possible to add squirters if you really wanted them) The question is, is it worth it for a 855 when there are currently much better designed diesels on the market today?


Other than the coincidental displacement, this motor is really nothing like the Big Cam 400 motors. But by golly, I'm gonna throw some boost at her anyway and see what she'll put out. I won't be pushing much more than 10-15 psi with this old girl.

And it should be fine


Not sure if you're saying you don't believe me that a bunch of these military 855's have blown up 30 miles or less out of the IronPlanet gate, but they have. I've seen it. It might not be on YouTube, but it happened.

You stated, quote;


(Blow up) which many have done just in stock form since they pretty much sat for the last 15 years

I stated that they shouldn't blow up from simply sitting. If an engine blows, theres a reason, but sitting usually isn't going to cause that unless something failed…either previously or after the fact.



With your HP vs. TQ formula, don't forget that HP is just a measurement of HP at a given RPM, but don't confuse that and think that you can find your max HP from your max TQ. You can find your HP at your max TQ RPM, but your MAX HP is going to be at an altogether different RPM where the TQ is lower (generally speaking). People seem to really struggle with this concept.


What many people don't realize is HP is a mathematical figure derived from torque and RPM. You can arrive at say 400HP (or pick any HP figure you like) by an infinite combination of different torque values and different RPM speeds. You can have a 400HP engine which produces very little torque, but spins it really fast, or you can have a 400HP engine that produces a ton of torque, spinning it really slow. Diesels are a perfect example of horsepower via high torque to low rpm, whereas gas engine horsepower is via low torque to high rpm.

HP and TQ varies at different RPMs. Yes, there is a point in the RPM range of an engine where each (HP/TQ) reaches a peak, (and both do not usually occur at the same RPM) but thats not what we were talking about. The formula reveals an interesting fact of engine physics. That any engine revving above 5252 rpm is usually producing more HP than its TQ, and any engine spinning below 5252 rpm is producing more TQ than it's HP. Only at exactly 5252 rpm are the two the same figure and this convergence isn't happening at peak RPM for either HP or TQ. The amount of HP & TQ are always dynamic, as an engine capable of higher rpms can still continue to produce more TQ beyond 5252 rpm, but the HP figure will always be greater than it's TQ figure and vise-versa for any RPM below 5252 rpm. What I want you to see is the "relationship" between the two.

Ed

pyrojoe22
03-14-2017, 11:34 AM
I don't remember which thread it was on, or what the details were exactly, but I'm pretty sure the NHC-250 block is completely different from any other 855 in the way you would add the oil squirters, making it near impossible/really difficult/expensive to do. I know that's vague, but you can always google it on steelsoldiers and read up on it.

Now if there were other models of the 855 that were turbo'd but didn't have oil squirters, I would really like to read up on their specs. If nothing else, they'd make a nice reference for the turbo size and the max boost/EGT that people run with them.

RXT
03-14-2017, 12:45 PM
I don't remember which thread it was on, or what the details were exactly, but I'm pretty sure the NHC-250 block is completely different from any other 855 in the way you would add the oil squirters, making it near impossible/really difficult/expensive to do. I know that's vague, but you can always google it on steel soldiers and read up on it.

A quick google search, shows the NHC-250 is part of the same design family as other "855" engines including the Big Cam 1, 2, 3 & 4. Many parts aren't interchangeable, but they do share the same or similar design features. I read in one place that there were later model small cam NHC-250s with piston squirters but couldn't confirm it elsewhere. So if true, it could be possible to add it to one that doesn't have the squirters. But it isn't rocket science either. A squirter could be built if you can tap into the oil pump, or get ingenious and somehow add in another oil pump exclusive for your squirters. An idea that does to mind is to search for an electric pump that can be mounted externally and plumbed thru the oil pan, for both the pick up and the squirters. But as mentioned, there are other options. You can help keep the pistons cool with an intercooler and/or water injection, and don't boost and feed fuel to high levels. That keeps the EGTs down, which in turn keeps the pistons from melting.

Ed

pyrojoe22
03-14-2017, 12:49 PM
Ed,

Are you going to be doing any of these mods yourself? Or are you just curious in general? No one ever posts back their results, so if you wanted to get started on the 855 turbo, we could at least have some data to compare to my 5.9 swap until I get time/money to do the 855 turbo mod.

RXT
03-14-2017, 01:57 PM
Nah, I got a 6BT stuffed in a Dakota 4x4 and thats what I've been playing with these days. Used to drive OTR and loved hearing stories about old Big Cams from the guys who drove them. Seeing that you live in Nebraska, if you ever get a chance, go next-door to Walcott Iowa, it's a bit far, but there's a truckstop there called Iowa 80, I remember they used to have big truck shows every year (I looked it up, apparently they still do…it's been about 15yrs since I've been out there)

Anyway, you're bound to see a few old school big rigs and maybe some will still be running these older engines. With a little luck you might find a small cam, probably chromed and turned up a bit. If you do, you might be able to pick the owner's brain about his build.

Ed

edpruss
03-14-2017, 07:54 PM
I think the Iowa show is very close to 4th of July.

Ed

Dougal
03-18-2017, 05:27 PM
Power and Torque for engines are simply different ways to measure the same result. Engine output.

From the torque curve you can calculate the power curve and vice-versa. The 5252rpm crossover only works for units of ft-lb and hp. Using any other units (say kW and Nm) the crossover occurs at a different point (9550 rpm).

RXT
03-21-2017, 12:22 PM
Power and Torque for engines are simply different ways to measure the same result. Engine output.

From the torque curve you can calculate the power curve and vice-versa. The 5252rpm crossover only works for units of ft-lb and hp. Using any other units (say kW and Nm) the crossover occurs at a different point (9550 rpm).

The basic physics behind my point is the same no matter which standard of measure you're using. Be it HP, Nm, kW or any other standard, the relationship with rpm and torque is the same.

Ed

char1355
03-25-2017, 09:04 AM
A lot of interesting info here, but for the most part these are big truck engines. To me the ideal engine would be a P pump 6CT 8.3. That one is already a turbo engine and the power can be turned up dramatically. This isn't discounting the 6bt idea. No problem getting it into the 300 HP range, but the torque might not be where you'd want. Cummins made the 6bt in 230 HP models with over 600 lb ft of torque. So with proper pump timing and the right cam grind you could have one of those in the 300 HP 800 lb ft torque range. Might even consider a twin turbo arrangement. There's really no basic limit to what can be done. It's just a matter of cost.

pyrojoe22
04-13-2017, 08:37 PM
I am starting to look into the details of this project a little closer now. Looks like for the NHC-250, I'd want to run an HT3B? It only struggles on the top end, so I don't see a small/quick-spooling turbo or compounds being necessary. Hoping I can get a helluva deal on some junkyard parts (manifolds/turbo/etc) off a small cam turbo 855.

For the 5.9, it looks like all 8.3 and 855 5-tons came with the SAE #2 bellhousing adapter. Should be able to find the bellhousing adapter/flywheel from a medium duty 5.9 truck. Then the 5 ton starter should bolt up. From there, the torque converter and tranny should all bolt right up. Hopefully the adapter and flywheel don't cost too much. Any suggestions what/where to look for these parts?