Whats' the Difference in Fuel Economy Between a Cummins 6.7L H.O. and Standard Output?

[Goose55]

Recalling a Youtube I watched of a Cummins lead engineer for Ram pickup engines, he said the standard output is engineered/ tuned for efficiency. How much more efficient is the standard output 6.7L over the high output version? Fuel economy difference?

 

[Billet Bee]

It was a huge differnce for me. Now I do understand that these 2 trucks were completely 2 different beasts so take that into consideration. Also the low gear will affect the mpg as well
2016 ram 2500. Srw 6.7 s.o. 373 gear. 20-24 mpg
2020 ram 3500. Drw 6.7 h.o. 410 gear. 12-15 mpg

The reason you buy a ho is if your hauling heavy trailers, which I am, then you don't worry about the fuel .

 

[jejb]

The folks I know that have owned both do complain about the loss of MPG's compared to the SO's they also owned. But they all haul heavy and often, and do appreciate the power.

 

[mtnrider]

I doubt there is any noticeable differences in mpg between the engine's themselves, the different transmission and gear ratio would have more impact.

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[Goose55]

I doubt there is any noticeable differences in mpg between the engine's themselves, the different transmission and gear ratio would have more impact.

.

How would the Chrysler 68RFE differ from the Aisin? They are both 6 speeds, I believe

 

[mtnrider]

How would the Chrysler 68RFE differ from the Aisin? They are both 6 speeds, I believe

Different gear ratios, different shift strategies,. If you drive them back to back you will feel a difference between the 2 in the way they drive and behave

 

[John Jensen]

The SO and HO have different compression ratios resulting from different engine components and then have different tunes. That alone would make a mileage difference The HO probably weighs more than SO. I don't believe the tranny differences have much, if anything, to do with mileage

 

[Goose55]

The SO and HO have different compression ratios resulting from different engine components and then have different tunes. That alone would make a mileage difference The HO probably weighs more than SO. I don't believe the tranny differences have much, if anything, to do with mileage

John, I see you have the HO w/ a 3.73 Axle. What is the best highway mpg you have gotten, empty?

 

[John Jensen]

John, I see you have the HO w/ a 3.73 Axle. What is the best highway mpg you have gotten, empty?

I'm Calibrateed tuned. Highway (not towing) I average 15.7-16mpg. Recently on a 525 mile stretch @ 75 mph I got 18.8 mpg with a +40 hp tune. Towing I am getting 10-12. My overall average to date is 13.9 mpg.
Keep in mind, my truck is only at 9700 miles and still breaking in. I noticed the first jump in mileage at approx 6000 miles

 

[Billet Bee]

I'm Calibrateed tuned. Highway (not towing) I average 15.7-16mpg. Recently on a 525 mile stretch @ 75 mph I got 18.8 mpg with a +40 hp tune. Towing I am getting 10-12. My overall average to date is 13.9 mpg.
Keep in mind, my truck is only at 9700 miles and still breaking in. I noticed the first jump in mileage at approx 6000 miles

Holy mackerel, and I thought I had low miles at 28k . We purchased ours at the same time, do you just drive it on weekends and pulling?
With my 410 gear and no tune I only get 8 mpg while towing at 75mph

 

[John Jensen]

Holy mackerel, and I thought I had low miles at 28k . We purchased ours at the same time, do you just drive it on weekends and pulling?
With my 410 gear and no tune I only get 8 mpg while towing at 75mph

I have a 2016 1500 Eco as my daily. My 2020 HO truck takes one 2000 mile, all highway, empty, trip per year. And 1-2 250 mile towing trips per year.

New, before I tuned it my towing was 9-10 mpg. I really don't know if my current 10-12 towing is due to being tuned or due to it breaking in. I'm inclined to believe it's due to breaking in.

 

[Billet Bee]

I have a 2016 1500 Eco as my daily. My 2020 HO truck takes one 2000 mile, all highway, empty, trip per year. And 1-2 250 mile towing trips per year.

New, before I tuned it my towing was 9-10 mpg. I really don't know if my current 10-12 towing is due to being tuned or due to it breaking in. I'm inclined to believe it's due to breaking in.

I'd agree, mine got better after more miles were logged

 

[Goose55]

Here's a guy driving a 2020 3500 standard output Cummins out onto the freeway. Going 75 mph, at only 1800 rpm, and fuel economy shows an impressive 20.2 mpg. My HO shows 1800 rpm at 65 mph. My old 1995 Tacoma 3.4 barely got 20 mph.

2020 Ram 2500 Laramie Crew Cab 6.7L Cummins Turbo Diesel - POV Review

Engine: 6.7L I6 Cummins Turbo Diesel EngineTransmission: 6-Speed Automatic 68RFE TransmissionCrew Cab 6-ft., 4-in. bedBase Price: $52,3500:00-6:18 Walkaround...

youtu.be

 

[John Jensen]

Here's a guy driving a 2020 3500 standard output Cummins out onto the freeway. Going 75 mph, at only 1800 rpm, and fuel economy shows an impressive 20.2 mpg. My HO shows 1800 rpm at 65 mph. My old 1995 Tacoma 3.4 barely got 20 mph.

2020 Ram 2500 Laramie Crew Cab 6.7L Cummins Turbo Diesel - POV Review

Engine: 6.7L I6 Cummins Turbo Diesel EngineTransmission: 6-Speed Automatic 68RFE TransmissionCrew Cab 6-ft., 4-in. bedBase Price: $52,3500:00-6:18 Walkaround...

youtu.be

That's strange. If the guy and you were both in 6th gear and both have a 3.73 rear end the rpm should be the same as the 6th gear ratios are the same.

 

[Goose55]

That's strange. If the guy and you were both in 6th gear and both have a 3.73 rear end the rpm should be the same as the 6th gear ratios are the same.

I have .410 gears in my HO dually.

 

[jejb]

Here's a guy driving a 2020 3500 standard output Cummins out onto the freeway. Going 75 mph, at only 1800 rpm, and fuel economy shows an impressive 20.2 mpg. My HO shows 1800 rpm at 65 mph. My old 1995 Tacoma 3.4 barely got 20 mph.

2020 Ram 2500 Laramie Crew Cab 6.7L Cummins Turbo Diesel - POV Review

Engine: 6.7L I6 Cummins Turbo Diesel EngineTransmission: 6-Speed Automatic 68RFE TransmissionCrew Cab 6-ft., 4-in. bedBase Price: $52,3500:00-6:18 Walkaround...

youtu.be

Actually, the truck in the video is a 2500. I got as much as 21.5mpg from my 18 2500 Cummins on a long, unloaded road trip, at a sustained 79-84mph (depending on the state I was going through). EVIC indicated 23.5mpg, so that was way off.

I assume my 22 2500 Cummins will do the same, but have not taken any unloaded road trips with it yet. Might not ever happen actually. We have other vehicles for that kind of thing that get 40+mpg. The one time I did it with my 18 was because I was just scratching an itch.

 

[howie12]

It seems to me another significant reason for the added fuel consumption/poorer mileage is the fact that the HO has more horsepower. Most people will use the additional hp sometime. COuld be faster acceleration, could be faster speeds up long grades could be heavier loads. Could be more passing and resultant higher average speeds because you can and on and on. Using more hp is doing more 'work' from a physics point of view and therefore it takes more fuel.

I see someone mentioned th higher compression ratio of th HO. That generally equated to greater efficiency but it is more complicated since th effective compression ratio (base plus boost) over the use cycle is the important issue and I do not have that info available.

Finally someone can probably find specific fuel consumption curves for these engines, unless Ram has kept them secret. All the commercial engine makers that I am aware of that make engines that compete for use in equipment, boats and large trucks make that info available. That info gives you the weight of ful consumed for each hp produced at a variety of specific RPMs. That info shows you two valuable pieces of info besides how much fuel it consumes. It shows the most efficient engine RPM in terms of fuel consumed per hp delivered which helps you figure out the optimum gearing from an efficiency point of vie which also has to be balanced by the hp able to be produced at various RPMs and the HP you need to do what needs to be done.

 

[mcv1]

I've got 35k on my 2020 HO. Even towing my 15k lb trailer 14 ft tall up I70 from Utah to Grand Lake at the speed limit I will average more than 12 mpg. Did about 14 mpg hauling to Yuma and back to Moab. Without a trailer on the highway, typically 80mph in UT and 75 in CO, I will average about 17 mpg. In a Moab/Denver RT today I am at 17.6. I get very close numbers hand calc or via dash. If anything my efficiency has dropped a bit since new, but I also have added 1000 lbs of tools, larger tires and a 2" lift. I'm very pleased with the fuel economy of my HO. Still a dealer tune, but they did flash from original factory settings to reduce the "surging" originally experienced when on cruise control on a very modest incline. I still have a bit of surging, but hesitate to let them touch it again given my currently great mileage.

 

[Goose55]

I've got 35k on my 2020 HO. Even towing my 15k lb trailer 14 ft tall up I70 from Utah to Grand Lake at the speed limit I will average more than 12 mpg. Did about 14 mpg hauling to Yuma and back to Moab. Without a trailer on the highway, typically 80mph in UT and 75 in CO, I will average about 17 mpg. In a Moab/Denver RT today I am at 17.6. I get very close numbers hand calc or via dash. If anything my efficiency has dropped a bit since new, but I also have added 1000 lbs of tools, larger tires and a 2" lift. I'm very pleased with the fuel economy of my HO. Still a dealer tune, but they did flash from original factory settings to reduce the "surging" originally experienced when on cruise control on a very modest incline. I still have a bit of surging, but hesitate to let them touch it again given my currently great mileage.

What exactly, MC, is this "dealer tune" you speak of? You attribute your great mpg to it? I'm interested.

 

[M376X6]

It was a huge differnce for me. Now I do understand that these 2 trucks were completely 2 different beasts so take that into consideration. Also the low gear will affect the mpg as well
2016 ram 2500. Srw 6.7 s.o. 373 gear. 20-24 mpg
2020 ram 3500. Drw 6.7 h.o. 410 gear. 12-15 mpg

The reason you buy a ho is if your hauling heavy trailers, which I am, then you don't worry about the fuel .

My 2022 3500 Dually 4X4 Limited with the Aisin and HO pushing 4.10 at 7,500 miles on the odometer is getting between 14 ad 15 with a little above and below depending how heavy my foot is. Of course with a 22 foot flat deck carrying an 85 W350 and a slide in camper I have gotten as low as 8 with a serious Wyoming headwind.