7.3 Godzilla F550 MPG/Range with large TC and SRW conversion

[Kepler]

Hi everyone,

I found a couple build articles of people who have taken chassis can F-550s and done the super single conversion along with having a custom bed made to hold the largest of truck campers. One used the 7.3 gas and the other used the 6.7 diesel. Both late model trucks post 2020. The gas build didn't have MPG numbers, but the diesel one claimed 12-14 which seems really impressive for a setup weighing close to 20k pounds and running on 41 inch tires.

From what I've read, people are pretty happy with the gasser with the exception of range relative to the diesel. I've found numbers on forums of around 8-10 when hauling a large camper, but that is on stock trucks with stock tires. Does anyone know what kind of MPG the 7.3 gets for this earth roamer type setup? I imagine it's really miserable with the large heavy tires/wheels along with the massive frontal area of the bigger campers. Anyone have any knowledge on this? Any thoughts on how wheel/tire size and weight affects mileage?

 

[andy_b]

Hi everyone,

I found a couple build articles of people who have taken chassis can F-550s and done the super single conversion along with having a custom bed made to hold the largest of truck campers. One used the 7.3 gas and the other used the 6.7 diesel. Both late model trucks post 2020. The gas build didn't have MPG numbers, but the diesel one claimed 12-14 which seems really impressive for a setup weighing close to 20k pounds and running on 41 inch tires.

From what I've read, people are pretty happy with the gasser with the exception of range relative to the diesel. I've found numbers on forums of around 8-10 when hauling a large camper, but that is on stock trucks with stock tires. Does anyone know what kind of MPG the 7.3 gets for this earth roamer type setup? I imagine it's really miserable with the large heavy tires/wheels along with the massive frontal area of the bigger campers. Anyone have any knowledge on this? Any thoughts on how wheel/tire size and weight affects mileage?

We have a ’24 F350 with the 7.3 - not exactly the same spec as the F550 but similar.

We weigh about 11,500lbs and get ~8.5mpg.

More weight and bigger tires = lower fuel economy.

 

[Kepler]

We have a ’24 F350 with the 7.3 - not exactly the same spec as the F550 but similar.

We weigh about 11,500lbs and get ~8.5mpg.

More weight and bigger tires = lower fuel economy.

I went back and found another article for the same rig and he states 7.5-8 with conservative driving and averaging 10 when using no ethanol fuel. That's at 18000 pounds, 41 inch tires and hauling a large northern lite. Not bad actually.

What are you hauling? I've been surprised by people having lower mileage with large campers than towing a 10,000 pound fifth wheel. Anyway that super single conversion and the liquid spring suspension together are very expensive. Also not accounting for the cost of the custom bed. Which got me wondering, what's the largest camper you can haul with an F350 chassis cab? If you were to build a "mini" version with an F350 CC, custom bed and perhaps a slight lift with 35s or 37s, normal suspension set up for the payload. Haven't seen that type of build from my searching. Only smaller campers.

 

[andy_b]

I went back and found another article for the same rig and he states 7.5-8 with conservative driving and averaging 10 when using no ethanol fuel. That's at 18000 pounds, 41 inch tires and hauling a large northern lite. Not bad actually.

What are you hauling? I've been surprised by people having lower mileage with large campers than towing a 10,000 pound fifth wheel. Anyway that super single conversion and the liquid spring suspension together are very expensive. Also not accounting for the cost of the custom bed. Which got me wondering, what's the largest camper you can haul with an F350 chassis cab? If you were to build a "mini" version with an F350 CC, custom bed and perhaps a slight lift with 35s or 37s, normal suspension set up for the payload. Haven't seen that type of build from my searching. Only smaller campers.

In order to know how much you’re going to weigh, you need to know how you’re going to use it - full 4 season, how many people overnight, level of independence on a trip, what kind of stuff do you do and what gear do you need, etc. Most 2+ person, year round setups seem to weigh ~12,000 at a minimum but get there in different ways.

Our build is here. We started with a 2000 F350 and recently upgraded to a 2024 F350. The 2000 is a 7.3 Powerstroke and probably got 10-12mpg. The 7.3 Powerstroke had a lot of additional power modifications and was significantly faster than the (currently stock) gas. Still, we do not miss it - the ’24 is one of the nicest cars I’ve owned and it was great to be able to spec it exactly how we wanted.

Not sure why you’d consider a 350 though. Our box is cab-width so it wouldn’t look right on a 550 chassis - otherwise, that is exactly what we would have replaced our old 350 with. I only offered our setup as point of reference, not as a “better” alternative. It really isn’t much cheaper since both trucks will basically the same mods ((suspension, wheels, tires flatbeds, etc) to make them usable as a basis for a camper. I’ve ridden in Liquid Spring equipped trucks - the ride is still very industrial. The adjustabllity for height and ride quality is pretty cool, but I couldn’t imagine spending that kind of money on it. I am positive if that was your budget, you could build a much nicer riding 550 using more traditional components customized for your setup.

Regardless of truck, if you could keep the weight down (~15,000lbs), the main advantage would be being able to stick with LT tires which are lighter, probably safer, and much cheaper than medium duty truck and military tires.

 

[rruff]

We have a ’24 F350 with the 7.3 - not exactly the same spec as the F550 but similar.
We weigh about 11,500lbs and get ~8.5mpg.
More weight and bigger tires = lower fuel economy.

What tires do you have?

Tire rolling resistance (bigness isn't the problem) x weight and frontal area x drag coefficient are the main loads. I'm averaging ~15 mpg with my Tundra on long highway roundtrips. Stand up flatbed camper, leveled, fat 35s, ~7600 lbs. I'd expect a difference, but not nearly that much.

 

[andy_b]

What tires do you have?

Tire rolling resistance (bigness isn't the problem) x weight and frontal area x drag coefficient are the main loads. I'm averaging ~15 mpg with my Tundra on long highway roundtrips. Stand up flatbed camper, leveled, fat 35s, ~7600 lbs. I'd expect a difference, but not nearly that much.

Currently 37x12.5-18 Toyo ATIIIs.

 

[rruff]

^I'd expect those to be decent, so I don't know. Should be way better than military tires anyway.

 

[Blackdogvan]

I learned an interesting factoid about the Godzilla 7.3 the other day & an interesting story about the unintended consequences of good intentions. In order to get a clean idle emissions check mark for the 7.3, Ford created a way via a solenoid pressure controller in the oil pressure circuit to lower the oil pressure at idle to reduce load/fuel consumption. Just at idle. This has now caused them to have a massive issue with lifters eating it due to low oil pressure at idle!

So try not to let your Godzilla idle too often to very long. Ford is working through the model years with a fix, might be worth a call to your dealer to see if your VIN is available for the recall. From what I understand it's just a programming update.

 

[Kepler]

In order to know how much you’re going to weigh, you need to know how you’re going to use it - full 4 season, how many people overnight, level of independence on a trip, what kind of stuff do you do and what gear do you need, etc. Most 2+ person, year round setups seem to weigh ~12,000 at a minimum but get there in different ways.

Our build is here. We started with a 2000 F350 and recently upgraded to a 2024 F350. The 2000 is a 7.3 Powerstroke and probably got 10-12mpg. The 7.3 Powerstroke had a lot of additional power modifications and was significantly faster than the (currently stock) gas. Still, we do not miss it - the ’24 is one of the nicest cars I’ve owned and it was great to be able to spec it exactly how we wanted.

Not sure why you’d consider a 350 though. Our box is cab-width so it wouldn’t look right on a 550 chassis - otherwise, that is exactly what we would have replaced our old 350 with. I only offered our setup as point of reference, not as a “better” alternative. It really isn’t much cheaper since both trucks will basically the same mods ((suspension, wheels, tires flatbeds, etc) to make them usable as a basis for a camper. I’ve ridden in Liquid Spring equipped trucks - the ride is still very industrial. The adjustabllity for height and ride quality is pretty cool, but I couldn’t imagine spending that kind of money on it. I am positive if that was your budget, you could build a much nicer riding 550 using more traditional components customized for your setup.

Regardless of truck, if you could keep the weight down (~15,000lbs), the main advantage would be being able to stick with LT tires which are lighter, probably safer, and much cheaper than medium duty truck and military tires.

The super single conversion without any specialized suspension is 20k+. The campers not being cab width is one of the reasons for having a custom bed made. I didn't come up with that because you have an F350, I thought of it before because it seems much simpler and less expensive to avoid the conversion which necessitates such large tires. But the payload of the 350 CC is "only" around 4700-5000 pounds so I'm not sure if you can manage to do this with something like a lance 960 or 975. I'm assuming regular cab, long bed and only 2 people. I'm not sure if that number is excluding or including a bed, but I assume it's the former.

 

[rruff]

The super single conversion without any specialized suspension is 20k+.

The rims are in the $700-$1250 range, each. I don't know what else you are including, but someone building a F350 will get rims and tires too... so the rim premium is the real cost.

It looks like Stazworks makes steel 17" rims, which seems like a good option if you are using LT tires. https://www.stazworks.com/steel-wheels

The campers not being cab width is one of the reasons for having a custom bed made.

Don't think I'm following you. Big commercial campers are ~96" wide but they fit on a typical bed. If you get a custom bed you can add a lot of external storage. They look better on a F450/F550 because the width is a better match.

 

[Kepler]

The rims are in the $700-$1250 range, each. I don't know what else you are including, but someone building a F350 will get rims are tires too... so the rim premium is the real cost.

It looks like Stazworks makes steel 17" rims, which seems like a good option if you are using LT tires. https://www.stazworks.com/steel-wheels


Don't think I'm following you. Big commercial campers are ~96" wide but they fit on a typical bed. If you get a custom bed you can add a lot of external storage. They look better on a F450/F550 because the width is a better match.

That number is from the people who do the conversion like buckstop. I'm not sure exactly what adds so much to the cost. It's even higher with labor.

And what I meant is that the large campers being much wider than the typical bed width makes the setup look kind of funny. Having a custom bed made for the width of the camper makes the whole thing look integrated. Not as "symmetrical" as an earth roamer or one of it's equivalents, but pretty decent.

Also, Lance made the altimeter which is based on the 855 and put it on an f350 as a showcase. Crew cab f350, regular bed, some upgraded suspension but otherwise normal. That's a 3000lb camper dry. I guess it's possible then?

 

[andy_b]

The super single conversion without any specialized suspension is 20k+. The campers not being cab width is one of the reasons for having a custom bed made. I didn't come up with that because you have an F350, I thought of it before because it seems much simpler and less expensive to avoid the conversion which necessitates such large tires. But the payload of the 350 CC is "only" around 4700-5000 pounds so I'm not sure if you can manage to do this with something like a lance 960 or 975. I'm assuming regular cab, long bed and only 2 people. I'm not sure if that number is excluding or including a bed, but I assume it's the former.

The Buckstop super single conversion includes everything, even the bumper. It is clearly spelled out on their website. They actually have a very easy to use configurator that spells out final cost, including labor. Pretty slick!

I’m not sure what you’re getting at about “campers not cab width.” The main reason these trucks run large tires is weight capacity lost by moving away from 19.5 or 22” wheels and their higher weight rated tires, not that the conversion itself. If you can keep it light enough, you could do a single conversion like the one @rruff mentioned above that uses LT-beaded tires.

Ultimately, any truck is going to benefit from the same upgrades - tires, wheels, suspension and the costs will be about the same (assuming equivalent levels of quality or customization).

The houses of EarthRoamers and similar are definitely wider than the cab - usually the track width or slightly wider of the rear axle. Maybe I misunderstood what you were saying about EarthRoamers aesthetic.

 

[Kepler]

The Buckstop super single conversion includes everything, even the bumper. It is clearly spelled out on their website. They actually have a very easy to use configurator that spells out final cost, including labor. Pretty slick!

I’m not sure what you’re getting at about “campers not cab width.” The main reason these trucks run large tires is weight capacity lost by moving away from 19.5 or 22” wheels and their higher weight rated tires, not that the conversion itself. If you can keep it light enough, you could do a single conversion like the one @rruff mentioned above that uses LT-beaded tires.

Ultimately, any truck is going to benefit from the same upgrades - tires, wheels, suspension and the costs will be about the same (assuming equivalent levels of quality or customization).

The houses of EarthRoamers and similar are definitely wider than the cab - usually the track width or slightly wider of the rear axle. Maybe I misunderstood what you were saying about EarthRoamers aesthetic.

Yes, minimum 26 thousand for the basic package with install. If the wheels are only a few grand by themselves, presumably the rest of what they offer is necessary for suspension geometry and whatever other considerations there are like rubbing.

I know the wheels have to be that size to hold that kind of weight. By symmetrical what I mean is it doesn't look like it's "spilling over the bed". All I'm curious about is what you can "get away with" without having to get into a class 5 then do this conversion. I talked to an owner of one of these rigs very recently and he used to carry a 5000 pound camper with a regular 1 ton. It was obviously too much. But if you're a single person or couple who are okay with something in the 3000 pound dry weight class and you're not carrying a lot of extra weight, you should be better off saving the cost and sticking with a 1 ton. So, a 1 ton with a chassis or flatbed mounted camper, mild lift and regular sized wheels/tires. It's not just the upfront cost, but the cost of replacing parts and maintenance.

 

[rruff]

...presumably the rest of what they offer is necessary for suspension geometry and whatever other considerations there are like rubbing.

None of it is "necessary" unless you get big military tires, and even then there are much cheaper ways to do it.

I'm fine with Buckstop going after the "spare no expense, here's the check" crowd, but if you want to use a F450-F550 chassis and you can keep your rear axle weight <~8,000 lbs (which would be at least 5,000 lbs added)... then the only added expense you have relative to a F350 is the more expensive rims... plus the extra price of the truck itself.

 

[Se7en62]

We have a ’24 F350 with the 7.3 - not exactly the same spec as the F550 but similar.

We weigh about 11,500lbs and get ~8.5mpg.

More weight and bigger tires = lower fuel economy.

That's good to know. We get the same mileage with my '19 6.2L F350 at 12,400 lbs on 37s.