: 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.