The inline Cummins motors are long. I know a guy with a 4BT in his EB and it fits but its tight. A 6BT wouldn't fit unless you want to make the rear valve cover double as your cup holder.

 

a 6bt will fit. It has been done but 4bts just fit better and produce more than enough grunt for an early bronco to be a lot of fun. There is one on dieselpowermag.com that has a 400+hp 4bt which is like in the 7-800lb ft range. I would love to have an early bronco with a 4bt in it.

 

The 4BT is definitely the most popular diesel swap for the Early Broncos.

However, Van Tumblin (a.k.a modman on cb.com) put an earlier 7.3L Powerstroke in one. See this thread:

Powerstroke EB - ClassicBroncos.com Forums

 

That 7.3 in an EB is awesome, but I'd hate to have to work on it in there.

 

All too big n heavy in my mind (1,000 lb?) for the EB. Guy @ Sterling, MA "BYOB" 4th ann. rally had one. Lots of mods to hold it up.
The 80s Jap motors too small n wimpy.
Wish this country got it together. Thought 'bout the 3.5 in the Liberty - but it's from a Heep n made in Italy.
The 300 I6 is about as close as possible but U gotta move the fire wall or radiator.

IT All depends on Application.
Mine's a work truck, sees bout 20-30% on road. I work my property, in the woods n swamp n plow in the winter. Use a konig PTO for a couppla implements. After 27 yrs of ownership I could see a little power boost but a back hoe motor? And anything larger, Hummm...

 

The 3.9L (4BT) Cummins 4 cylinder is relatively short and weighs about 700 lbs. That's a really nice setup in the little Broncs. Engine longevity would probably be more than the average human life span, and fuel mileage is awesome!
I'm trying to recall the 4BT specs off my head, it's 120 hp, and 350 ft/lbs at 1500 rpm? That's similar hp, but nearly 100 ft/lbs more than the 300 motors make. Gearing is no longer a thought when you have that much power down low. Cooling the motor is easy, the stock radiator with relocated spouts is all you need. I'm running the 6BT on the stock non-a/c(the smaller one) radiator with no fan shroud and the fan is about 5" away from the rad, and it stays right at 180, even when idling.
I love diesels.

p.s. I moved my whole drivetrain back 4 inches from the stock location, in order to move some of the 1/2 ton of engine weight off the nose of my '78 Bronc, and with the indent in the firewall, it fit in there better than it did in the '91 dodge parts truck I took it from. It's been years since I sold my '77 Bronc, and I don't recall what the firewall looks like on those EBs, but is there room to move the motor back any if you were to use a 4BT? If so, 2 or 3 inches would make up for the extra 100 lbs of weight from the 4BT engine.

 

Yea and that is just in stock form. I think its actually a little lower on the hp numbers like 105 or 110 but still at 40mpg that makes up for whatever the weight takes away. Also they can be turned into quite a lil powerhouse. Theres a couple sites around that are just for 4bts and they have gotten them up in the 400hp region which usually means about 800 lbft. Those engines still get better mileage than any gas bronco

 

Oh yeah, I can imagine the mileage you could get from that light truck with a 4BT.. It would make an awesome daily driver.
My full size '78 with the cranked up 6BT has enough power to smoke the 35" tires at 30 mph in high gear and it still averages 20 mpg. It would get better highway mileage if I could swap in higher gears, but unfortunately the highest ratio available for the reverse cut Dana 44 front axle is the stock 3.50s.. But even so, I'm content with having twice the power and twice the mileage, too. One problem with a Cummins Bronco though is all the import "race" cars that get in the way and stuck in the grill like bugs.. hah

 

6BT pics:


Like a glove!


These really are big motors. 1000 lbs wet. And for the record, they do look better in Dark Ford Blue than they do in factory Cummins black.

 

yea theres a guy on fsb.com that has a 600hp 6bt thats gettin 21mpg. I wish I could afford to do that.

 

To get 600 hp you need something like a compound turbo setup, which is really expensive, and a built up P pump and injectors. Plus head studs, performance camshaft, big intercooler, huge downpipe, and performance lift pump. Once you get the 6BT on such huge steroids, then you have to have a transmission built that will even consider dealing with 1200 ft/lbs of torque. I got a quote from my transmission guys at Dynamic, and it was somewhere around $3000 for my C6 to be built that strong. Then you have to have custom super strength driveshafts/u-joints built, and finally, at least in my case, Dana 60 rears. The D44 front in my truck would scream maniacally for a few millionths of a second before scattering shrapnel everywhere under that much power. As cool as it might look, especially when filmed and uploaded to youtube, I'd prefer to avoid such things.
That much power costs thousands upon thousands of dollars.
I don't have anywhere near that kind of money right now, but boy it's nice to think about.. heh

 

if you are a member on fullsizebronco.com you should hit up GOS. He has a 600 hp cummins in his obs bronco and he has a stock ttb up front and a stock rear end. He doesnt have that much in it I think. It looks awesome and the way he drives it holds up just fine

 

I will check into that, thanks

 

6BT pic
like a glove

No intercooler? Or is in on after these pic (looks almost, not quite completed in these pic).

 

Nope, no intercooler yet, my motor is an early '91, the I/C didn't come out until later that year. One benefit of the non-I/C 6BT, is that they have larger injectors from the factory. I have plans to install a powerstroke I/C, bigger turbo housing and make my own intake from a 3" exhaust elbow. That should bring a very big increase in power and fuel mileage.