1969 Bronco Build

[Digger]

In the larger bore Cummins world, we say not to even calculate FE until 40-50k miles on the engine for what it's worth.

I'll keep that in mind. I would really like to know where the mileage is, but I was banking on a slight improvement as the engine wears in.

It's laughable, but I haven't gotten any good data yet because the engine just isn't burning enough fuel.

[Sanders]

It's laughable, but I haven't gotten any good data yet because the engine just isn't burning enough fuel.

When we were in Alaska for Ultimate Adventure 2019, the R2.8's on the trip would still have over half a tank as others were already burning through jerry cans. Not a huge deal when you're in an off road park or a road trip with gas stations every few miles. A much bigger deal when you are in remote Alaska and don't see a gas station for 2-3 days! Every Cummins got to play tow truck to the gas stations at least once with the V8's.

When we first announced the program, I watched many forums with folk trying to do the math to justify the swap by fuel savings payback. Although you get there eventually, the fuel MPG gain is less of a fuel cost saving thing and more of a range comfort for me at least.

[nuffsaid]

This was one of my main reasons for the swap, RANGE and not having to lug around gas cans, add to that the fact I usually have an aux diesel tank mounted in my pickup makes it sooooo nice.

[Digger]

When we were in Alaska for Ultimate Adventure 2019, the R2.8's on the trip would still have over half a tank as others were already burning through jerry cans. Not a huge deal when you're in an off road park or a road trip with gas stations every few miles. A much bigger deal when you are in remote Alaska and don't see a gas station for 2-3 days! Every Cummins got to play tow truck to the gas stations at least once with the V8's.

When we first announced the program, I watched many forums with folk trying to do the math to justify the swap by fuel savings payback. Although you get there eventually, the fuel MPG gain is less of a fuel cost saving thing and more of a range comfort for me at least.

So true. After selling off the old engine and extras I didn't need and fabbing a lot of parts myself, I was only out about $500 to purchase the R2.8. That's about 6 months ROI for me. Throw in materials and parts I needed to to complete the swap and total ROI will be ~3 years. Not bad for my situation.

All that aside, it was about building a better rig. Range was a huge benefit, especially towing. I was facing the need to add 2 jerry cans to the rear bumper for certain trips. While it looks cool, 10 gallons of gas hanging off the back bumper is not exactly safe, even in a minor rear-end collision. (And diesel is inherently safer to transport too)

[DieselJeep]

I bought pretty much everything as a kit and my ROI in a $5,500 vehicle plus $20k in goodies including adapter, engine, fuel tank, fixing stuff that was broken vs dropping $45k for the closest thing I could find that was released to the US market. When I was first trying to justify costs, I tried that with fuel, but it mostly comes down to the right fit for the task at hand. With $40k+ vehicle costs, I'm not going to buy something that isn't the right "fit". If I'm getting a 4x4 that I want to last a long time, get good range, and do some towing and hauling (and range is a big deal since filling up ever 100 miles is much different than 250 or 300 and sometimes access is horrible at some stations), I want lots of low RPM torque, MPG does get you more range without having to have massive fuel tanks (anything under 400 mile range IMO is kind of annoying), and diesel engines are typically very reliable and tend to allow you to limp out when gas engines will just stop. Also I don't like all the plastic and stuff in new vehicles. I prefer my dash to look like a cockpit, with easy to access gauges and no windshield to remove to get to my heater core type stuff (my step dad was told by Honda that they would have to PULL THE ENGINE to replace the fog light, though I think this had to be a miscommunication somewhere).

Before my swap I could tow my Jeep with my truck with the 5.9 Cummins and get about 13-14 mpg vs driving the Jeep and getting 11 mpg and I was always looking for places to top off and with a small vehicle like a TJ, gas cans get very annoying to deal with all the time I need that space for other stuff, especially in the heat after being bounced around all day. And then comparing that experience to some time I spent in India, where everything was very practical and everything was diesel, it's just so hard to go back to gas engines for anything but specialty racing, which I don't do.

On top of that we've had 1 vehicle fire that took out several acres that probably wouldn't have occurred with a diesel vehicle and another truck that started to catch fire, but in an area that we were able get it put out without much damage (though I lost my pants in that fire, which was kind of funny after the fact).

[DieselJeep]

While it looks cool,

I was joking with my wife that one of the "benefits" of having the Toyota Tacoma and not the Hilux, is that we can show off our Rotopax. I told her I was going to mount 2 in front of her windshield just to pull a Ricky Bobby inspired Instagram post.

If your R2.8 or other diesel powered vehicle is running with V8s on the trail, it might actually save time to bring some gas for them, so we don't have to tow them as much.

I do like V8s, but I haven't missed anything related to a V8 compared to having a R2.8 powered rig. The only benefit would be that I really don't mind destroying a cheaper V8 that is plentiful and easy to swap out or just scrap the vehicle.

[Digger]

Driving a mix of 75 mph interstate and stop-n-go commuter traffic, Bronco achieved 23 mpg on the first tank.

Not bad for a brick on 37s

[Digger]

2 month update:

- Miles driven: ~4000

- Average tank: 23 mpg

- Worst tank: 22 mpg

- Best tank: 24.5 mpg

- First trip off road went real well. The Cummins is a solid performer on the trail. Good low end torque, feels unstallable in the rocks, runs 176-180F all day and sips fuel. Even on a 9 hour trail day, the Bronco still average 22 mpg on that tank.

- Towing the camper: The Cummins did better than expected. I was apprehensive that 161 HP would be enough to push two bricks down the road, but I could generally cruise at 65-70 mph, which is plenty fast around the mountains of Colorado. Not only was I able to keep up with traffic, on some hills I was even the one doing the passing.
Towing the camper would drop my F250's mileage from 20 to 13. With the Bronco, I was pulling a solid 17mpg. I was able to make a 500 mile trip on less than a tank and a half.
The bad news is on the really steep, long grades at full throttle, the cooling system is not quite keeping up. While the radiator could keep up with a 375HP V8, I think the additional heat load of the CAC is too much. Right now I'm focusing on improving the air flow through the radiator by plugging the gaps and improving the venting.

[DieselJeep]

How much city driving are you doing?

How much does your camper weigh?

Do you have the most up to date tune?

[Digger]

How much city driving are you doing?

How much does your camper weigh?

Do you have the most up to date tune?

Driving about 60% city. Very stop and go commute right now.

Camper doesn't weight much at 2700 lbs, but presents a significant wind load. Basically I get the same mileage towing a 7000 lbs flatbed or a 2700 lbs camper with my 7.3 PSD

What is the most up-to-date tune? I should have the 310 lbft tune right now.

[DieselJeep]

When I first got the R2.8 mine had a different tune and I had to drive to Cummins and get them to update the tune. It's my understanding that the stock world tune is 360 ft lbs.

My tires and my rack have dropped my MPG, but it's still a big improvement compared to a gas vehicle. Rack gave me about a 10% reduction and tires seem to be around 5%. Now I tend to get around 20 mpg city and 22 or 23 highway, but I still don't have enough data after my gear swap and lift. Plus there's something not right in the rear axle I just rebuilt.

[Digger]

1 year(ish) update:

Still running strong with zero issues so far, haven't needed to change anything yet.

Mileage is slightly better with average tank at 23.5 mpg and best tank at 25.1 mpg.

[rud404]

Thank you for the 1 year update, its good news. About how many miles did you drive in the past year?

[Digger]

Thank you for the 1 year update, its good news. About how many miles did you drive in the past year?

About 6000 miles.

[nuffsaid]

Awesome build! You did an outstanding job!!!!

[Digger]

Did some light snow wheeling the other day: