Performance/Efficiency versions of Cummins 6.7L

[ShinerBock]

It appears that Cummins is doing the same thing to their 6.7L engines that they have been doing with the larger on highway engines for the past few years by making a performance version and an efficient version of the same engine. The performance versions of their engines have higher power levels at the expense of lower compression ratio to keep NOx levels within standards. The efficient versions generally have higher compression ratios at the expense of power. For those that do not know, compression ratio has a direct correlation with an engines efficiency and how much NOx it produces at a given power output. Essentially the more power you produce, the more NOx you create so to combat this you have to lower compression ratio which reduces efficiency.

With the 2019 Cummins, the 400 hp "performance" version with the Aisin comes with a 16.2:1 compression ratio(down from 17.3:1 from 2007-2018) while the 370 hp "efficient" version with the 68RFE comes with a 19.0:1 compression ratio. However, it appears Ram is not calling them performance or efficient version like Cummins does with their other engines.

There are no official reviews on the fuel mileage difference, but I would wager it is around a 1-2 mpg(could be more) difference between the two which is similar to the difference percentage wise in the larger engines. Maybe Ram/Cummins is finally listening to many people here who have stated that these trucks make plenty of power for what the average consumer tows, and to start focusing on making the engine more efficient instead of increasing power/towing ratings at the expense of efficiency.

What do you think? If you had a choice and towed less than 20k lbs, would you choose the 400 hp/1,000 lb-ft performance version at the expense of 1-2 mpg or go with the 370 hp/850 lb-ft at the expense of 30 hp and 150 lb-ft and higher than 20k tow rating?

[ShinerBock]

FishOnOne wrote:

ShinerBock wrote:
Both engines can easily and reliably make well over factory power levels

I hear this statement from time to time but I have to ask why did Cummins change the internals to handle the 1,000 ft/lbs. I would have expected no internal changes if this were true.

What internals were changed? My Cuumins Quckserve shows the same internals. The main thing that changed was a CGI block to shave weight and a CP4 to increase fuel pressure to allow more power while meeting emissions. CGI blocked allows you to use less material due to it being a stronger material pound for pound so less can be used while having the same strength similar to how less "high strenght" material is being used in the frames.

The other reason for these changes may also be for future performance gains similar to how Cummins made to the 5.9L and 6.7L over the years by only changing engine tuning, fuel systems, heads, and turbo without changing any internals.

If it wasn't for these emissions requirements and future CAFE regulations coming to HD trucks that are bring mpg requirements to these truck classes. There are plenty of current 6.7L engines making well over 1,000 lb-ft with hundreds of thousands of miles on the clock.

[Me_Again]

Cummins12V98 wrote:
I will bet towing them side by side they will get similar mileage. No way 1-2 mpg different. Running solo maybe.

Did you miss the non towing in my post? Chris

[Cummins12V98]

FishOnOne wrote:

ShinerBock wrote:
Both engines can easily and reliably make well over factory power levels

I hear this statement from time to time but I have to ask why did Cummins change the internals to handle the 1,000 ft/lbs. I would have expected no internal changes if this were true.

HEY he used to work for CUMMINS. :B

[FishOnOne]

ShinerBock wrote:
Both engines can easily and reliably make well over factory power levels

I hear this statement from time to time but I have to ask why did Cummins change the internals to handle the 1,000 ft/lbs. I would have expected no internal changes if this were true.

[Cummins12V98]

That empty mileage is no different than my 15 4.10/AISIN DRW. Mountain driving I am at 7.5-8.5 but overall average HAND calc I am 9-9.5 33-35k combined.

So not any big difference as this topic suggests.

[ib516]

Here's a mpg test of a 2019 with the 1000 lb-ft engine towing 16k vs. unloaded.
CLICKY

"Our Utah test route covered steep grades, freeways, highways, city streets and low-speed curvy mountain roads. Elevation ranged from 4,500 feet to 5,400 feet with some steep sections and some relatively flat ones.

We ran the loop twice: first with the truck empty except for the driver and the second loop with a PJ equipment trailer loaded to 16,000 pounds with a 1,600-pound tongue weight and attached to the truck using a weight-distribution hitch. The trailer was loaded heavy and low, thus not presenting much wind resistance, which is a major factor for fuel economy, especially at speed. This load range requires the driver to have a commercial driver's license, and I have one.

For both runs, the air conditioning was set to max, the transmission was set to Drive, the rear air suspension was in the default position and everything else was left alone. When towing, the same was applied, but Tow/Haul mode was turned on and the exhaust brake was set to auto. There was no manual shifting and no idling beyond sitting at red lights.

Empty of everything but the driver, DOT safety kit and fifth wheel hitch, the Ram 3500 ran the route netting 13.8 calculated mpg using 4.52 gallons of fuel; the truck's onboard trip computer read 15.1 mpg. When loaded with the 16,000-pound trailer, it averaged 9.5 calculated mpg using 6.58 gallons of fuel. This time, the truck's computer read 9.9 mpg, which was much closer than the empty run, but still off.

We were surprised to see the low unladen fuel mileage, even with the equipped 4.10 axle ratio. During our 2018 One-Ton Heavy-Duty Truck Challenge, the single-rear-wheel Ram 3500 with the 3.42 axle ratio returned 16.9 mpg empty and 9.9 mpg when towing; granted, that different test is not directly comparable, but it did have similar laden results."

[ShinerBock]

eHoefler wrote:
Compression is only one part of the puzzle. The lower compression motor has a higher output turbo, which translate to higher compression when running hard. More air + more fuel = more power. As far as fuel economy, I am with in 1/2 mile per gallon of my old truck, pulling the same trailer and the same roads. With just over 2,000 miles on this beast. As miles get put on, I suspect the milage will only get better, like my 4 previous Rams.

The lower compression allows for more power while staying within NOx emissions. You could not have that same power output with the 19.0:1 compression ratio engine and still remain NOx legal. I have to check the specs on Cummins Quickserve when I get back to work, but I don't believe the turbos are different just the engine tuning. Both engines can easily and reliably make well over factory power levels, but they cannot do it and stay emissions legal.

[eHoefler]

Compression is only one part of the puzzle. The lower compression motor has a higher output turbo, which translate to higher compression when running hard. More air + more fuel = more power. As far as fuel economy, I am with in 1/2 mile per gallon of my old truck, pulling the same trailer and the same roads. With just over 2,000 miles on this beast. As miles get put on, I suspect the milage will only get better, like my 4 previous Rams.

[ShinerBock]

Cummins12V98 wrote:
I will bet towing them side by side they will get similar mileage. No way 1-2 mpg different. Running solo maybe.

The larger efficiency engines get better fuel mileage than the performance versions even when towing. An engine with a higher compression ratio will be more efficient than the same engine with a lower compression ratio at all engines speeds and loads due to its higher thermal efficiency.

This higher efficiency is represented as a percentage so a 20% increase for example of a higher number will be be greater numerically than a 20% increase of a lower number. For example, a 20% increase of 15 mpg is 18 mpg while a 20% increase of 10 mpg is 12 mpg.

[Cummins12V98]

I will bet towing them side by side they will get similar mileage. No way 1-2 mpg different. Running solo maybe.

[Me_Again]

ShinerBock wrote:
It appears that Cummins is doing the same thing to their 6.7L engines that they have been doing with the larger on highway engines for the past few years by making a performance version and an efficient version of the same engine. The performance versions of their engines have higher power levels at the expense of lower compression ratio to keep NOx levels within standards. The efficient versions generally have higher compression ratios at the expense of power. For those that do not know, compression ratio has a direct correlation with an engines efficiency and how much NOx it produces at a given power output. Essentially the more power you produce, the more NOx you create so to combat this you have to lower compression ratio which reduces efficiency.

With the 2019 Cummins, the 400 hp "performance" version with the Aisin comes with a 16.2:1 compression ratio(down from 17.3:1 from 2007-2018) while the 370 hp "efficient" version with the 68RFE comes with a 19.0:1 compression ratio. However, it appears Ram is not calling them performance or efficient version like Cummins does with their other engines.

There are no official reviews on the fuel mileage difference, but I would wager it is around a 1-2 mpg(could be more) difference between the two which is similar to the difference percentage wise in the larger engines. Maybe Ram/Cummins is finally listening to many people here who have stated that these trucks make plenty of power for what the average consumer tows, and to start focusing on making the engine more efficient instead of increasing power/towing ratings at the expense of efficiency.

What do you think? If you had a choice and towed less than 20k lbs, would you choose the 400 hp/1,000 lb-ft performance version at the expense of 1-2 mpg or go with the 370 hp/850 lb-ft at the expense of 30 hp and 150 lb-ft and higher than 20k tow rating?

Interesting that you post this today, as a lunch today at our Veteran's Habitat for Humanity build I was sitting next to a guy that has a 2016 2500 RAM and he quoted non towing best mileage numbers 1-2 MPG better than my 2015 3500 HO gets. Chris

[twodownzero]

IdaD wrote:
I'd take the more efficient option. My Cummins is rated 370/800 and I've never encountered a situation where I thought I needed any additional power.

Mine is rated at 325/610 and I certainly could use more going up the Rockies. It just creates heat an wear though; probably safer to back it down.

I'd buy the more efficient option. A 10% hit in power is nothing. Both will do the job, one will just do it faster.

[ShinerBock]

I would take the efficiency one as well and just modify and tune it for more power afterwards to get the best of both worlds. If Ram added the 8HP to the efficient version then I would be very tempted to sell mine and get one. I would love to see the fuel mileage that thing gets deleted.

[IdaD]

I'd take the more efficient option. My Cummins is rated 370/800 and I've never encountered a situation where I thought I needed any additional power.

[SidecarFlip]

All hinges on the fluctuating price of fuel. With the current trend of states jacking up fuel taxes (especially on diesel) to finance their dwindling coffers, 1-2 mpg might become a big deal down the road.