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Discussion Starter #1
I'm toying around with the possibility of pulling out the GM 6.5 diesel & dropping a Cummins 4bt into an ex-military, (m998) Humvee (a.k.a. Hummer H-1).

I have heard of people putting a 6bt in one, I know while a 6bt swap brings the Humvee immense power and reliability improvements, but a 6bt's rocker arm covers almost touch the top of the engine compartment, requires upgrading the transmission, axle shafts, brakes, & geared hubs, and the mpg really doesn't improve much if at all.

With that in mind, has anyone swapped a 4bt into a Humvee?

1) Does it fit better?

2) Does performance improve over the original GM 6.2 / 6.5?

3) Does MPG improve? (I refer to the mpg & performance using straight diesel, not WVO or alternative fuels)

4) Do you have to upgrade the rest of the drivetrain? like for a 6bt?

5) Are there 4bt conversion kits for Hummer H1's/Humvees?
(Transmission adapters, Crossmembers, Engine Mounts, Pump/Compressor/Alternator Brackets, etc)

Most of my knowledge is on paper or from putting together specs & stuff I find on the internet, and (on paper) a 4bt swap looks like it can be a very good idea for a Humvee (or Hummer H-1), but I have yet to hear (or find a well-illustrated build thread) from anybody who has actually DONE such a swap.
 

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Without having done it, just my back-of-the-napkin impressions;

1) It would have to; shorter by 2 cylinders, so where the Hummer hood gets tightest toward the front, you don't still have rocker covers anymore.
2) 4BT is 120HP, 250 ft-lbs, give or take. GM 6.2 / 6.5 is 130hp, 330 ft-lbs, give or take. But I think you can push a 4BT more than a GM 6.2 diesel and it will live.
3) 4BT might push 900lbs wet. GM 6.2 is actually pretty similar, from a quick search. Less cylinders, same load, same power output, so better MPG?
4) Nah....same power output as the 6.2l.
5) If it has a Chevy bellhousing there are many, many 4BT's out of Chevy's that have those adapters on them already.
 

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Discussion Starter #3 (Edited)
Thanks for the reply Ryan P !

This whole idea began when I learned of a 4bt swapped into an '85 Chevy blazer CUCV that went from 17mpg with the 6.2 to 28mpg and equal performance with the more durable 4bt connected to a beefed up 700r4 transmission.

I also saw a youtube video of someone in northern California who did put a 4bt into his m998 humvee, but he gave no details besides driving it around and showing off the new engine sound it makes, and another guy who did the same swap and shows off his Humvee now runs on wvo, but again, no other details.

On paper it looks like the 6.2 and the 4bt (with an injector upgrade)'s output are *almost* a match, so . . .

I wonder if the minor differences on the 4bt's output can damage the m998 hummer's stock axles and geared hubs, I was asking for anybody who knew.

I wonder if a 4bt hummer will get the same mpg improvement as the 4bt blazer did?

And as far as a physical fit in the hummer's engine bay, the hummer has a cutout in the firewall that I saw almost scrape the top of a 6bt installed in it, I heard somebody say once that the 4bt is not as tall as the 6bt, is that right?

Without having done it, just my back-of-the-napkin impressions;

1) It would have to; shorter by 2 cylinders, so where the Hummer hood gets tightest toward the front, you don't still have rocker covers anymore.
2) 4BT is 120HP, 250 ft-lbs, give or take. GM 6.2 / 6.5 is 130hp, 330 ft-lbs, give or take. But I think you can push a 4BT more than a GM 6.2 diesel and it will live.
3) 4BT might push 900lbs wet. GM 6.2 is actually pretty similar, from a quick search. Less cylinders, same load, same power output, so better MPG?
4) Nah....same power output as the 6.2l.
5) If it has a Chevy bellhousing there are many, many 4BT's out of Chevy's that have those adapters on them already.
 

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... I heard somebody say once that the 4bt is not as tall as the 6bt, is that right?
The 6bt is a 4bt with 2 extra cylinders. The height of the engine is the same for both, many parts interchange. The length of the 6bt is obviously greater. Remember, actual dimensions depend on how the accessories (ie, turbo, fan, alternator, AC compressor, piping to the engine, etc).
 

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has anyone swapped a 4bt into a Humvee?
I have, here's my BT: http://www.4btswaps.com/forum/showthread.php?13924-1986-Military-HMMWV-4BT-Conversion-Work-in-Progress&highlight=1986+hmmwv

Sold the truck and I miss it, so I'm building another hmmwv 4BT and an aggressive tune.

You'll need to upgrade the old stock th400/np218 to a 4L80e/np242amg, aftermarket trans controller, driveshafts, and reposition your front driveshaft to clear the pan. Other than that, that's it. Parts (billet or bread van adapters, engine mounts, isolators, and xmembers, driveline parts from a 94-03 hummer h1) can all be available on eBay.

Hope that helps,
Phil
 

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I have, here's my BT:
Sold the truck and I miss it, so I'm building another hmmwv 4BT and an aggressive tune.

You'll need to upgrade the old stock th400/np218 to a 4L80e/np242amg, aftermarket trans controller, driveshafts, and reposition your front driveshaft to clear the pan. Other than that, that's it. Parts (billet or bread van adapters, engine mounts, isolators, and xmembers, driveline parts from a 94-03 hummer h1) can all be available on eBay.

Hope that helps,
Phil
Im currently working on a 4bt swap on a 1998 HMMWV. I have gotten things all good but having trouble clearing the oil pan. Any ideas or how you managed to do it without repositiong the front dif over to the left?

Kinda stuck at the moment. Any imput would be great. thanks again. Glad to see others have succeedeed.

Crauly
 

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Turbo the 6.5 and call it a day. Nothing wrong with the 4BT but it will not be a good combination behind the 3 speed auto. The 6.2/6.5 military motors are pretty reliable. You can buy the turbo system for a M1114 or M1151 for cheap. It's not the best turbo out there but it will get the job done and is very easy to install. Turn the injection pump up two flats and install an pyro gauge. If you need more power play with the timing and maybe install a 6.5 turbo pump and continue to tune it. It's not hard to get 200hp/450tq out of a well tuned 6.5 and it has a wider power band then a 4BT.
 
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