- 1,046
- 45
- 48
- Location
- Syracuse, New York
Beware. I posted most of this in Engine Information Please thread last night. It was intended for here. I cleaned it up a bit but looks rather rambiln. David did say "Let the discussions continue....."
Maximum speed (w/Maximum Payload and Towed Load) - 45MPH (page 1-17)
Maximum speed (w/Maximum Payload only) - 56MPH (page 1-17)
The reduced speed when fully loaded w/trailer may have more than one reason. While the authority/ designers may be trying to protect the engine they may also factor in that fact that a fully loaded combined vehicle is much more difficult to control.
I think TM's need to keep text brief so as not to 'overcomplicate' the issue. They prob. also are assuming a worst case situation. The may also figure the drivers may, more often than not, be young and inexperienced.
As for running at 2600rpm all day:
These were built for hauling loads for relatively short distances, perhaps in combat, probably more often than not on poor roads( if any). When the army needs to send stuff cross-country they use the commercial freight system w/trucks better suited to the purpose.
As a group we all seem to have a different agenda. Some might be found taking lawn chairs and a cooler down 8 lane I-95, in 80+mph traffic, on the way to Aberdeen... Can the Ld/LDT/LDS take it? Sure. Will it cut it's lifespan? Sure. But many can afford this as it still may take 2 lifetimes to wear it out. Those here that run cross country may wear theirs out a bit sooner but that may be OK as there will be some great stories for the grandkids...
Here is the truck I drove today, a non-typical commercial tractor trailer. I say non- typical because this spend half the day as a city pedal truck and the other half as a road unit. It is a no frills, no sleeper, small engine, work truck. The engine is the modern version of the ubiquitous Mack 673. It is a 05' Mack Vision - engine EM7-317(?) - engine is 728ci, turbo , intercooler, 278,000miles (currently), will run to ~1million miles. ~9mpg(?)loaded or empty.
Redline (dash) - 2200rpm
Visor info - Operating range 1100-1800rpm, do not exceed 2100rpm
No-load governed speed -2100rpm
Max rpm in gear:
1st-4th - 2000rpm
5th - 1925rpm
6th - 1725rpm
7th - 1425rpm (64mph max)
Looking at these numbers you can see on the big roads the engine runs at very low speed. This maximizes both fuel economy and engine life. The engine is geared to run just past torque peak so any additional load(grades) will cause it fall towards peak torque.
This is why commercial truck engines are different, and why they last longer.
Those here running multi-fuel at 2600rpm (or above) are probably doing so because it's inconvenient and expensive to have a custom made low ratio high gear set made (is there one?). Then, the task of installing it. New gearing, or perhaps a different tranny, may be what is really needed. JimK
p.s. additions:
Torque rating of a similar EM7-250 (an 02'' was last one I checked ) was 1040lb*ft at 1200rpm (though all these seem to be turned down from there).
Mack called these 'High Torque Rise". Torque builds fast at 1000 and is mostly in by 1100. It does rises a tad more, ~1200 is the peak. Above that torque fades slowly as rpms rise.
corrections:Correct the current miles 278K (not 250K) and Manufacturer's stated (visor) operating range 1100rpm - 1800 (not 1000-1800). 7th 1425rpm (not 1475)
Maximum speed (w/Maximum Payload and Towed Load) - 45MPH (page 1-17)
Maximum speed (w/Maximum Payload only) - 56MPH (page 1-17)
The reduced speed when fully loaded w/trailer may have more than one reason. While the authority/ designers may be trying to protect the engine they may also factor in that fact that a fully loaded combined vehicle is much more difficult to control.
I think TM's need to keep text brief so as not to 'overcomplicate' the issue. They prob. also are assuming a worst case situation. The may also figure the drivers may, more often than not, be young and inexperienced.
As for running at 2600rpm all day:
These were built for hauling loads for relatively short distances, perhaps in combat, probably more often than not on poor roads( if any). When the army needs to send stuff cross-country they use the commercial freight system w/trucks better suited to the purpose.
As a group we all seem to have a different agenda. Some might be found taking lawn chairs and a cooler down 8 lane I-95, in 80+mph traffic, on the way to Aberdeen... Can the Ld/LDT/LDS take it? Sure. Will it cut it's lifespan? Sure. But many can afford this as it still may take 2 lifetimes to wear it out. Those here that run cross country may wear theirs out a bit sooner but that may be OK as there will be some great stories for the grandkids...
Here is the truck I drove today, a non-typical commercial tractor trailer. I say non- typical because this spend half the day as a city pedal truck and the other half as a road unit. It is a no frills, no sleeper, small engine, work truck. The engine is the modern version of the ubiquitous Mack 673. It is a 05' Mack Vision - engine EM7-317(?) - engine is 728ci, turbo , intercooler, 278,000miles (currently), will run to ~1million miles. ~9mpg(?)loaded or empty.
Redline (dash) - 2200rpm
Visor info - Operating range 1100-1800rpm, do not exceed 2100rpm
No-load governed speed -2100rpm
Max rpm in gear:
1st-4th - 2000rpm
5th - 1925rpm
6th - 1725rpm
7th - 1425rpm (64mph max)
Looking at these numbers you can see on the big roads the engine runs at very low speed. This maximizes both fuel economy and engine life. The engine is geared to run just past torque peak so any additional load(grades) will cause it fall towards peak torque.
This is why commercial truck engines are different, and why they last longer.
Those here running multi-fuel at 2600rpm (or above) are probably doing so because it's inconvenient and expensive to have a custom made low ratio high gear set made (is there one?). Then, the task of installing it. New gearing, or perhaps a different tranny, may be what is really needed. JimK
p.s. additions:
Torque rating of a similar EM7-250 (an 02'' was last one I checked ) was 1040lb*ft at 1200rpm (though all these seem to be turned down from there).
Mack called these 'High Torque Rise". Torque builds fast at 1000 and is mostly in by 1100. It does rises a tad more, ~1200 is the peak. Above that torque fades slowly as rpms rise.
corrections:Correct the current miles 278K (not 250K) and Manufacturer's stated (visor) operating range 1100rpm - 1800 (not 1000-1800). 7th 1425rpm (not 1475)
