F450 vs Ram 3500 DRW tow vehicle

4x4ord wrote:

ShinerBock wrote:

4x4ord wrote:
The rule is the same for all turbo charged diesel engines... throttling down and gearing up for light loads saves fuel. I was listening to some farmers talk about their tractors equipped with IVT (infinitely variable) transmissions. During light load operations the computer slows the engine down below 1200 rpm and some guys over ride the comperter because they can't wrap their head around the idea of working an engine at such low rpm.

For light loads yes, and I have been saying that. However, heavy loads is another issue and utilizing over over 40% of an engines rated power at an rpm isn't a light load placed upon the engine. It is even worse in the real world because rated power is an idealistic environment at 70F, at zero ft of elevation, and low humidity which is how the SAE dynos are done. Realistically, your are not attaining rated numbers most of the time at it is even more of a load being placed on your engine at that rpm.

40% of what an engine is capable of producing a a certain rpm is definitely a light load.... of course it's a light load .... it's only a 40% load.:S

I thought the rpms we were talking about were 1,600 and 2,000 rpm, not 2,800 rpm? The PSD may make 475 hp at 2,800, but not at the rpms you and Grit dog were talking about. As you said earlier,the max amount of power the PSD makes at 1,600 rpm is 320hp and 380 hp at 2,000 rpm. Even less in the real world. So at these rpms, you are asking for more than 40% of what the engine is capable of giving you at these engine speeds.

ShinerBock wrote:

4x4ord wrote:
The rule is the same for all turbo charged diesel engines... throttling down and gearing up for light loads saves fuel. I was listening to some farmers talk about their tractors equipped with IVT (infinitely variable) transmissions. During light load operations the computer slows the engine down below 1200 rpm and some guys over ride the comperter because they can't wrap their head around the idea of working an engine at such low rpm.

For light loads yes, and I have been saying that. However, heavy loads is another issue and utilizing over over 40% of an engines rated power at an rpm isn't a light load placed upon the engine. It is even worse in the real world because rated power is an idealistic environment at 70F, at zero ft of elevation, and low humidity which is how the SAE dynos are done. Realistically, your are not attaining rated numbers most of the time at it is even more of a load being placed on your engine at that rpm.

40% of what an engine is capable of producing a a certain rpm is definitely a light load.... of course it's a light load .... it's only a 40% load.:S

4x4ord wrote:
The rule is the same for all turbo charged diesel engines... throttling down and gearing up for light loads saves fuel. I was listening to some farmers talk about their tractors equipped with IVT (infinitely variable) transmissions. During light load operations the computer slows the engine down below 1200 rpm and some guys over ride the comperter because they can't wrap their head around the idea of working an engine at such low rpm.

For light loads yes, and I have been saying that. However, heavy loads is another issue and utilizing over over 40% of an engines rated power at an rpm isn't a light load placed upon the engine. It is even worse in the real world because rated power is an idealistic environment at 70F, at zero ft of elevation, and low humidity which is how the SAE dynos are done. Realistically, your are not attaining rated numbers most of the time at it is even more of a load being placed on your engine at that rpm.

The rule is the same for all turbo charged diesel engines... throttling down and gearing up for light loads saves fuel. I was listening to some farmers talk about their tractors equipped with IVT (infinitely variable) transmissions. During light load operations the computer slows the engine down below 1200 rpm and some guys over ride the comperter because they can't wrap their head around the idea of working an engine at such low rpm.

Here is is the same 8.3L Cummins for a marine application. Notice how different the fuel consumption rate is......



Here is the same 5.9L for low speed steady state industrial applications. Again, same engine, but different application and cam profile.

4x4ord wrote:
^^^^ Nebraska tractor tests has tested hundreds of turbo charged diesel engines and have reported that all obtain better fuel economy by throttling down and gearing up under light load conditions.

Running the Powerstroke at 2000 rpm would qualify as throttling down but if you notice the article defines a light load as one that requires less than 65% of an engine's peak Hp. So for the 2020 Ford that means a light load would be a load requiring under 308 hp. At a light load such as that, the article says reduce rpm by 20 to 30%. So in other words if the F450 is pulling a light load .... say one that requires under 300 Hp... it would be good to throttle it back to between 1820 and 2080 rpm. If I was towing loads that require 300 hp I'd want the 4.30 gears.

Not necessarily, A Powerstroke and Cummins 6.7L are made for a completely different purpose and have completely different cam profiles than that of a tractor. Most tractors like our John Deere 4430 is tuned/design for low rpms so its cam profile is made so that it makes peak power and efficiency at lower rpms and low speeds. Similar to this 4.5L chart below.



The PSD and CTD on the other hand are made for higher rpms and higher speeds so the cam profile was made for better efficiencies in these higher ranges. Not only that, but their turbo efficiency maps are as well. You are using engines designed for a totally different purpose and saying it applies to on road engines.

^^^^ Nebraska tractor tests has tested hundreds of turbo charged diesel engines and have reported that all obtain better fuel economy by throttling down and gearing up under light load conditions.

Running the Powerstroke at 2000 rpm would qualify as throttling down but if you notice the article defines a light load as one that requires less than 65% of an engine's peak Hp. So for the 2020 Ford that means a light load would be a load requiring under 308 hp. At a light load such as that, the article says reduce rpm by 20 to 30%. So in other words if the F450 is pulling a light load .... say one that requires under 300 Hp... it would be good to throttle it back to between 1820 and 2080 rpm. If I was towing loads that require 300 hp I'd want the 4.30 gears.

4x4ord wrote:
You don't want to be lugging an engine but the closer you are to running it at peak available power the better fuel economy it will achieve. So if an RV requires 175 HP to cruise down the highway, then running the new Powerstroke at 1600rpm (55% load) makes more sense than running it at 2000 rpm (46% load). I just did a quick search and came up with this
article that explains the point I am trying to get across:

Yeah, on one engine. Every engine is tuned/designed differently with different cam profile, turbo efficiencies, max fuel pressure, injector events, and so on. The cam itself plays a huge role at not only when the engine makes peak torque/power, but also its peak efficiency. I can show you another engine chart as the one above on a different Cummins engine and its fuel consumption rate would be completely different spots because it was tuned/design for a completely different purpose.

You don't want to be lugging an engine but the closer you are to running it at peak available power the better fuel economy it will achieve. So if an RV requires 175 HP to cruise down the highway, then running the new Powerstroke at 1600rpm (55% load) makes more sense than running it at 2000 rpm (46% load). I just did a quick search and came up with this
article that explains the point I am trying to get across:

4x4ord wrote:


This is very useful info but it needs to be interpreted properly. So the 5.9 was capable of achieving its best fuel economy at 2000 rpm BUT that is under heavy load. Under heavy load it was able to make 175 hp at 2000 rpm. If its fuel consumption was measured at 2000 rpm and it was only loaded to 50% of its capability it certainly would have been using more fuel than .334 lbs per hphr. I'm talking about slowing an engine down under light load conditions to improve fuel economy.
If that old Cummins had a demand on it of 80 hp, I would call that a light load, It could easily produce 80 hp at 1500 rpm and I would be willing to bet it would achieve better fuel economy producing 80 hp while running at 1500 rpm than it would running 2000 rpm with a 80 hp demand on it.

The new Powerstroke is a totally different animal. At 1600 rpm it can produce 320 HP.... 380 hp at 2000 rpm. I am saying 175 hp demand on a new Powerstroke engine qualifies as a very light load. It doesn't need anywhere near 2000 rpm to produce 175 HP. In other words 175 HP to the new Powerstroke is like 80 HP was to the old 5.9 Cummins.

And I think it is very few RVs that even require 175 HP to pull them down the highway at 70 mph. So I'll stick with my claim that 4.30 gears are not the right gears for RVers wanting a new Powerstroke. If you want a F450 for the wide front axle it is understandable but the 4.30 axle unfortunately comes with it.

According to your numbers, the 175 hp needed is 55% of max available power at 1,600 rpm and 46% of max available power at 2,000 rpm.

I would not call that a very light load or even a light load in terms of what you are demanding from the engine at those rpms. To me, below 15% of max capability at X rpm is a very light load.

I think you are looking at this in terms of max potential of the engine itself instead of max potential at a certain rpm. That is not how it works. At wide open throttle(full load) at 1,600 rpm, all the PSD can make according to your numbers is 320 hp. Half load at that rpm would be 160 hp. It does not do its max of 475 hp at that rpm so you have to look at it terms of how much of a load it is at that rpm, not at peak hp numbers of the engine.