tractor diesels vs. pickup diesels

[Erik_in_Hoyt]

the other thing to look at is what RPM you get the HP.
that Dodge cummins diesel rated for 350 HP may only be producing 75 HP at 2000 RPM -- which is no-load highway speed. You don't get that 350 HP until you're above 6000 RPM.
My "210 HP" 3.7L V6 gas motor is only putting out 50-75 HP at normal driving RPMs as well. If I want to see that power, I've got to leave it in 3rd while driving at 70. (I spent half an hour looking at torque vs HP graphs for all the engines available to the Ram series last saturday while the dealership was
"working" on my truck)
The real interesting thing to me looking at their graphs was the power discrepancy in the big motors between manual and auto trannys -- on at least one of their truck setups the highest output on a manual is lower than the starting HP when the motor is paired with an auto tranny.

 

[ccsial]

You see this in medium duty v. light duty truck applications, too. A 5.9L Cummins diesel may crank out 325Hp stock from the factory in a Dodge pickup, but in a medium duty F-650 dumptruck

Dodge claimed originally that the 5.9 was derated so as not to tear up the drive train in the pickups. I have a 97 RAM Cummins rated at 225hp. It has mechanical injection and I'll keep it till I'm gone.

My boat has two 5.9 Cummins marine diesels that are rated at 300hp each. They can run at a good load for many hours on end. Much more load than my truck.

I suspect that one reason for the high displacment to HP ratio it to make the HP with a large torque component rather than RPM. Tractors have a fair amount of power at low RPM. Some of the old gas treactor engines only ran at 2500 compared to cars at 6000 or more.

 

[john_bud]

the other thing to look at is what RPM you get the HP.
that Dodge cummins diesel rated for 350 HP may only be producing 75 HP at 2000 RPM -- which is no-load highway speed. You don't get that 350 HP until you're above 6000 RPM.
.

Uh, Dude - we are talking about diesels - not gas engines. They don't rev to 6000. Can't go that high, flame propagation is too slow to allow those rpms.

The Dodge cummins is probably getting 550 ft-lb of torque at 1250 rpm's, and holding that and more up to the red line of 3200 (ish - I don't know the exact red line for them).


Google up on diesel engines and review - interesting stuff.

jb

 

[ccsial]

Uh, Dude - we are talking about diesels - not gas engines. They don't rev to 6000. Can't go that high, flame propagation is too slow to allow those rpms.
jb

John: If you read closer you will see I was comparing car gas engines to tractor gas engines. Tractors run much slower and therefore have larger displacements to make more torque. Same is true for diesels. Torque is proportional to HP X RPM. Larger displacement for more torque and less RPM. That was the original question.

Honda may change all the diesel theory. The following from Car & Driver:

From the Tokyo auto show comes confirmation that Honda’s 2.2-liter diesel engine will come to the U.S. installed in the 2009 Accord. The aluminum engine is fairly conventional in that it has a balance shaft, dual overhead cams, and high fuel pressure. The redline is around 4500 rpm; that’s where the Euro-spec diesel Accord we drove topped out.

 

[patrick_g]

.
My "210 HP" 3.7L V6 gas motor is only putting out 50-75 HP at normal driving RPMs as well. If I want to see that power, I've got to leave it in 3rd while driving at 70. (I spent half an hour looking at torque vs HP graphs for all the engines available to the Ram series last saturday while the dealership was
"working" on my truck)
The real interesting thing to me looking at their graphs was the power discrepancy in the big motors between manual and auto trannys -- on at least one of their truck setups the highest output on a manual is lower than the starting HP when the motor is paired with an auto tranny.

Just because a graph says you can get X HP at Y RPM that doesn't mean that you do!

Shifting to a lower gear to run more RPM to "DEVELOP" more HP when cruising along constant speed on level road at or below the speed limit is BALDERDASH!

Simple example: Put tranny in neutral and run engine to 6000 RPM. The ACTUAL HP being produced is NOT what the graph shows.

The graph shows how much HP COULD BE produced at that RPM if the load were increased to hold the rpm at that level with FULL THROTTLE applied. Otherwise you are developing much less HP. This is true for gas, diesel, steam, etc.

While driving at a constant speed the various drags of aerodynamics, friction, rolling resistance of tires etc adds up to exactly match the HP the engine is putting to the road, otherwise you would be speeding up or slowing down. Therefore the HP developed while cruising at a constant speed is the SAME irrespective of the gear you are in and RPM required.

This is true whether or not a magic conveyor is involved.

Pat

 

[Z-Michigan]

Uh, Dude - we are talking about diesels - not gas engines. They don't rev to 6000. Can't go that high, flame propagation is too slow to allow those rpms.

The Dodge cummins is probably getting 550 ft-lb of torque at 1250 rpm's, and holding that and more up to the red line of 3200 (ish - I don't know the exact red line for them).

On a 2006 Dodge Ram/Hemi, peak torque of 605 ft-lbs is at 1900rpm. Peak horsepower of 310 is somewhere around 2500 rpm. Redline is at 2900 rpm, and while I haven't tested I think fuel cutoff is about that speed too. I don't think ours has ever been over 2500rpm in any use, including pulling a heavy trailer up mountains. The turbo whistle starts sounding like a steam engine though!

The Dodge's Cummins is very similar to the ISB motor sold for commercial trucks and sometimes sold with fairly close ratings. However, I still wouldn't try and run it at max hp for more than a few minutes.

As John noted very few diesels operate at high rpm - most have redlines of 4000rpm or less.

 

[Egon]

Just for interest the service manager at the dealership which sold me a 96 Dodge cumin's with auto said I could run it all day at 2300 RPM. Surprisingly that's the same RPM I've found works best for loaded towing with the OD locked out. It does get kinda boring sitting behind the wheel for days at a time listening to your ears rumble!

Aren't those little engines that make a buzzing sound that are used in model airplanes a diesel?? They turn over at alarming rates of speed. Probably make my chainsaw jealous.

The Cumin's will self destruct somewhere approaching 4000 Rpm or even lower.

 

[turbo36]

This is true whether or not a magic conveyor is involved.

Pat

You aren't trying to revive the "Will it take off" thread are you?

 

[Erik_in_Hoyt]

apologies - obviously I was confusing numbers from all the different graphs I looked at a week ago and was trying to remember.

 

[art]

A way we look at them which actually came from an oil manufacturer is 30-60-90, An auto is 30 percent of power use all the time to get down the road. The truck is 60% all the time and a tractor is 90% all the time. These are not exact and do vary from time to time as we've seen engines rated for 10,000 hours go 18,000 hours in low stress or load situations.Think all oils are the same? Not! We get to see many engine failures from engines that are using truck or auto engine oil in the tractors. Normally they are well below or close to half the engines lives that have had the appropriate oil in them.