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Why are there no serious HD Gas engines that could compare to a HO Cummins?

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truckin-on

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I just returned from a 1600 mile round-trip towing an enclosed car trailer with my '16 3500 HO CC SRW. Running 70-75mph or so, averaged ~11.3 mpg. Diesel around here is currently nearly $2/gal more than gas, and when you add DEF and oil changes and fuel filter changes, etc, the running costs of a diesel are crazy more expensive than a gasser. But there are no comparable RAM gassers that will tow over ~17K of trailer! Ford is king of the gasser hill currently, but they pale in comparison to the Cummins HO. The Cummins is certainly a great engine, and a very capable puller, but seriously, it would make way more financial sense to build a 8L+ monster gasser that would compare with the Cummins. I know it can be done, and financially it has to be pretty compelling I'd think.

I towed for quite a few years with a 454 Chevy 3500, and it got the job done and never complained. Certainly the Cummins I replaced it with was way more capable, but also more expensive to run.

I love the Cummins and just ordered a '23, but if there was a viable option, I'd go for gas in a heartbeat!
 
What kind of fuel milage do you think could be expected with an 8+ liter enginr that makes 750 foot pounds of torque? My guess would be 6-7 mpg when working and 11-12 unloaded. Just a guess of course, but I wouldn't think that would be very attractive. I ran a Ford 460 for 20 years, I don't miss that part
 
Highcountry said:
What kind of fuel milage do you think could be expected with an 8+ liter enginr that makes 750 foot pounds of torque? My guess would be 6-7 mpg when working and 11-12 unloaded. Just a guess of course, but I wouldn't think that would be very attractive. I ran a Ford 460 for 20 years, I don't miss that part
Click to expand...
My 6.4 only got 11 unloaded
 
Hard to say. These days, with fuel injection, cylinder deactivation, VVT, etc, I suspect you could get something pretty close to current emissions controlled diesel mileage. Perhaps 20% less? But considering the cost per mile premium of the diesel, the running cost would have to be considerably cheaper. With my 7.4L gasser I averaged ~7-8 mpg towing heavy. With the same trailer and my 2011 Cummins I was getting 9-10. Certainly better, but not astonishingly so.
 
truckin-on said:
I just returned from a 1600 mile round-trip towing an enclosed car trailer with my '16 3500 HO CC SRW. Running 70-75mph or so, averaged ~11.3 mpg. Diesel around here is currently nearly $2/gal more than gas, and when you add DEF and oil changes and fuel filter changes, etc, the running costs of a diesel are crazy more expensive than a gasser. But there are no comparable RAM gassers that will tow over ~17K of trailer! Ford is king of the gasser hill currently, but they pale in comparison to the Cummins HO. The Cummins is certainly a great engine, and a very capable puller, but seriously, it would make way more financial sense to build a 8L+ monster gasser that would compare with the Cummins. I know it can be done, and financially it has to be pretty compelling I'd think.

I towed for quite a few years with a 454 Chevy 3500, and it got the job done and never complained. Certainly the Cummins I replaced it with was way more capable, but also more expensive to run.

I love the Cummins and just ordered a '23, but if there was a viable option, I'd go for gas in a heartbeat!
Click to expand...

I would give a thought or two concerning a big travel trailer…
 
The issue with a gas engine is that you have a few losses which a Diesel does not have.
- Throttle losses. In a gas engine you need a throttle because fuel needs about lambda 1 to run well. Diesel runs at much higher lamda values no problem.
- Thermal efficiency with a high compression ratio on the Diesel. Typically 16-18. Gas engines would knock, the gasoline 87 has a tough time handling his high CRs.
- Diesels run Turbos and they convert heat into gas exchange. On many gas NA engines the pistons need to suck air into the cylinder while heat just goes out of the exhaust.
- Gas engines cool with fuel. At very high loads you might have to inject more fuel to keep your piston, valves, Turbo, etc cool. Especially the Turbo gas engines are pretty bad here.

The big 8l gas would need to be throttled a lot when you just go straight. Better due to a more unthrottled condition would be a small 3l 4cylinder engine with a long stroke but that might rev higher than the 8l. The trend goes to low revving Turbo gas engines which are small in displacement. Small cylinder count, long stroke would be best but people do not want to have that.
 
we had a dodge 2wd manual dually with the V10 and one of Ford's F250 with a V10 in it...waaayyy back in the day. the Ford wasn't really set up to pull heavy of course...that dodge v10 was just fun to drive though...almost like a supped up go cart, but like the old 454 Chevys, didn't see a gas station it didn't like. I think loaded down with a gooseneck full of cattle about 7-8mpg was all you could really expect get out of of it. didnt keep it long though as the diesels just made significantly more sense back then
 
I just parted ways with my Chevy 8.1 liter and it pulled my 12k load fine. But 9-12 mpg over it's lifetime was as good as it got.

Now I'm in the diesel camp and getting 16-19 early in it's life plus no comparison in ability to tow the same load. It's a big difference in the entire experience.
 
What got me thinking about this, again, was reading about the 672/1000 Chevy crate engine. 1004 HP @ 6,600 RPM, 876 LB-FT @ 5,600 RPM, naturally aspirated. Clearly not a truck engine, but imagine the possibilities! The current Hemi and large Ford gasser are modern engines, that I believe could scale-up to be a viable diesel alternative.

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In any event, no choices other than a Cummins HO for me at the moment, so that's why I have a '23 on order... I'm just not happy about the extra initial costs, additional weight, and higher running costs with the diesel cost premium, DEF, and maintenance costs. For me, it would be nice to eventually have a gasser alternative.
 
If they would put a turbo on the 6.4 then we would really have something.
 
The Ford 7.3 Godzilla is quite the motor. I had a 6.4 in a 2016 2500 and it was good for running around and got 14-15 with 37 on it, 373 axles. However Im not sure I would want to tow heavy with it. After owning a TRX, I've learned quite a bit what modern gas engine need to do to cool not only the engine, but cats. The TRX would go in cat over temp mode which would run extremely rich, in the 10s AFR sometimes high 9s. This was to cool the cats and causing abysmal MPG. Now I know its a different animal but it doesn't change if you're looking for a workhorse 8L, concept will still be the same
 
I think you will find that when towing capacities pass 10-12K gas engines just don't make sense. Their powerbands are all the upper RPM ranges and they just guzzle fuel when tasked will pulling big #'s.
 
Highcountry said:
What kind of fuel milage do you think could be expected with an 8+ liter enginr that makes 750 foot pounds of torque? My guess would be 6-7 mpg when working and 11-12 unloaded. Just a guess of course, but I wouldn't think that would be very attractive. I ran a Ford 460 for 20 years, I don't miss that part
Click to expand...
That sounds about on par with my 2021 Power Wagon.
 
truckin-on said:
Hard to say. These days, with fuel injection, cylinder deactivation, VVT, etc, I suspect you could get something pretty close to current emissions controlled diesel mileage. Perhaps 20% less? But considering the cost per mile premium of the diesel, the running cost would have to be considerably cheaper. With my 7.4L gasser I averaged ~7-8 mpg towing heavy. With the same trailer and my 2011 Cummins I was getting 9-10. Certainly better, but not astonishingly so.
Click to expand...
I think you're moving the ball here. In your opening post, you said you got 11.3 with the HO. That would be better with an SO, BTW. But if you take 7mpg for a big gasser under the same load, that is close to a 40% drop in mileage. So if regular was $3.50 a gallon, diesel would have to be $4.90 to break even. And if you're talking unloaded, I can do 21.5mpg hand calculated at 80mph on the highway with my SO. My gas 3/4 ton's were 12 and rarely 13 doing the same thing. But for towing in the current environment, it is close. For a little money one way or the other, I'll keep the Cummins though.

Oh, you also need to consider the oil change intervals are further apart on the Cummins too, which drives down the maint cost.
 
Lets not forget about accessibility to fuel and support for larger fuel storage.

If I am towing a 40ft camper, there are very few option for filling up at a gas station comfortably. Every fill up has to be planned, the station scouted, and hope for the best.

Diesel? Roll into your closest truck stop and fill up at the big-boy pumps. Use your fleet card. On your way.


There are a ton of aftermarket fuel tanks for diesel. Its safer to store and it is more stable to store for longer periods of time.
 
gimmie11s said:
Dont worry guys, pretty soon we won't need to choose between gas or diesel.

We'll only get to read about "the good ol days" at each 5 hour stop while we recharge after towing just 80 miles.

Gonna be great
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Seriously though, imagine what a properly designed well thought out diesel electric hybrid HD could be like. Going down hill? Who needs an exhaust brake, just dump everything into batteries and use that to blast you up the next hill. Towing an RV? Dump the excess power into the RV battery bank.

If we’re willing to take the 900# weight penalty of a 6.7L why not a slightly smaller engine and a big bank of batteries?

Hell, treat it like a diesel-electric locomotive and decouple the engine from the drivetrain entirely, just using it as a big generator.

I don’t think we’re there with technology today, but battery tech is improving rapidly, it won’t be far off.
 
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