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Old 02-14-2013, 12:52 PM   #1
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Throttle Use with Diesel & "Lugging"

This may sound like a silly question but here goes....

With my cars and even my Winnebago Workhorse vehicles I didn't "floor" it for normal acceleration. Generally I would slowly add throttle as I accelerated. Now, I have a 400 HP Cummins and not a whole lot of miles on it yet. One thing I have noticed is that it doesn't seem to like to be slowly accelerated in the same way I did my gasser. If I gently added throttle, it seem to take a rather long time to get to speed.

So, the last couple times I have driven it I nearly floor it until I get to speed. Is that typical? I suppose the fact that the engine is in the back and doesn't make the same noise I am use to might be playing a little trick on my perception.

Also, in reading items about climbing big hills I see references to allowing the engine to lug a little bit. I'm not quite sure I understand that term or what it really means. I would appreciate some opinions on that.
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Old 02-14-2013, 01:06 PM   #2
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Don,
A diesel is at its best when operated a little above the RPM of max torque.
It also is at its best under med to heavy load when the fuel is at max if needed.
Now before someone has to reach for their heart med's, due to the limited cooling
we see in our RV's you sometime have to run a higher RPM to keep engine and
exhaust temp within limits.
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Old 02-14-2013, 01:13 PM   #3
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wb is giving you good advice...
torque is what moves our heavy things...
my peak torque is at 1600 rpm, so I try to stay between there and 2000 for best performance and mpg...

your engine will be different and if a turbo,
the nature of turbo's is that they need some boost to get out of their own way


the great thing about turbo deezles though is tuning can change the response of the engine to YOUR preferences.... good luck !
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Old 02-14-2013, 02:09 PM   #4
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Lugging as defined by Cummins, as I recall, is the application of Wide Open Throttle below torque peak. Turbo charged diesels make boost by converting the heat of the exhaust through the turbine to spin the compressor, hence the turbo-charger. To get heat you have to add fuel. Typically you will not see max boost at torque peak. For example, on my ISC Torque peak is at 1450. Max governed RPM is ~2200. Best hill climbing is done between 1950 and 2150, its also where I see max boost.

Operating technique: If you look at the graph of torque vs hp you see that from Torque peak torque slowly drops off as HP rises. As RPM drops as you climb the hill the torque rises, down shift should occur at torque peak this will occur until sufficient power is developed to climb the hill at a lower gear. This is also best economy. Best rate of climb occurs when RPM is kept 1950-2150 on my engine. LimFac is engine coolant temp. Below 5k you should have sufficient cooling to walk the hills. Above 5k requires a slightly different technique.

Bottom line; drive your boost and your foot controls boost.
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Old 02-14-2013, 03:00 PM   #5
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No engine should ever be operated very long while it is lugging. You can't remember the graphs and charts while you drive, but you can determine at what RPM peak torque occurs. When you are climbing a grade, you want to keep the RPM at or above the peak RPM.

One very practical way to determine if the engine is lugging is if you depress the accelerator and the RPM does not increase the engine is lugging -- it doesn't matter what the RPM is. If that condition occurs, increase RPM by gear shift or slow down. Do what is necessary to make the rig responsive to accelerator action. If it is, the engine isn't lugging. Lugging puts the greatest strell on the engine.

All the best!
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Old 02-14-2013, 03:48 PM   #6
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All great advice so far.

It took me a while to learn that it was OK to let the engine seem like it was lugging a bit and that I didn't need to have my foot to the floor and the RPM screaming like in a gas rig.

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Old 02-14-2013, 03:50 PM   #7
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Not sure about your workhorse but your Cummins is all electriclal inputs so called fly by wire, just takes a little time to get used to it.
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Old 02-14-2013, 03:54 PM   #8
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All great advice so far.

It took me a while to learn that it was OK to let the engine seem like it was lugging a bit and that I didn't need to have my foot to the floor and the RPM screaming like in a gas rig.

Rick
Going from a gasser to Diesel is different. Thing to remember "Diesels don't Accelerate, they Gain Momentum"
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Old 02-14-2013, 04:58 PM   #9
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Going back to our transit bus driving days, in most buses, if we didn't mash the throttle to the floor in accelerating from a stop, we'd never been able to keep a schedule. In the older buses before drive-by-wire and hill-holder switches, it was taught to prevent roll back (a real no-no for transit buses), you were supposed give the brake pedal a full application of air and then immediately mash the throttle treadle to the floor when starting from a stop on a uphill incline. Since our motorhomes do not have a hill-holder switch, we now do that in our own rig if on an incline stopped at a traffic light as a full application of air on the brake pedal will hold the coach for a second until getting the foot on the accelerator treadle.

As has already been said, nowadays, it's all drive-by-wire throttle so there is no harm in flooring the pedal to get up to speed. Actually, even with the old air throttle and linkage throttles, there was no harm in flooring the accelerator pedal.

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Old 02-14-2013, 06:23 PM   #10
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Quote:
Originally Posted by Sky_Boss View Post
This may sound like a silly question but here goes....

With my cars and even my Winnebago Workhorse vehicles I didn't "floor" it for normal acceleration. Generally I would slowly add throttle as I accelerated. Now, I have a 400 HP Cummins and not a whole lot of miles on it yet. One thing I have noticed is that it doesn't seem to like to be slowly accelerated in the same way I did my gasser. If I gently added throttle, it seem to take a rather long time to get to speed.

So, the last couple times I have driven it I nearly floor it until I get to speed. Is that typical? I suppose the fact that the engine is in the back and doesn't make the same noise I am use to might be playing a little trick on my perception.

Also, in reading items about climbing big hills I see references to allowing the engine to lug a little bit. I'm not quite sure I understand that term or what it really means. I would appreciate some opinions on that.
Skyboss -- here's an interesting experiment for you to try. Have your cruise control set for 55mph. Accelerate from a dead stop, and accelerate as you would with the fuel pedal, once babying it like you did with the gasser, and a second time mashing it down.

Now try it again, and engage your cruise control once you get past it's preset low speed, probably about 25-30mph. You will find the cruise control is as agressive as if you mashed the fuel pedal. The cruise is the most intelligent system in your coach w.r.t. engine and transmission control (not so in an automobile). It won't do anything to hurt the engine/transmission, as its computer controlled.

For me, the moral of the story is that diesels spool up slowly, and since they're all electronic, fly-by-wire, no concern around full throttle on acceleration from a start-up from stop. They're smarter than the driver, and pretty much bullet proof.

In fact, diesels w/ Allison tranny have a learning mode on how you drive, accelerate, and will time the tranny shifts accordingly, the longer you drive it. If you want faster off the line, it might not upshift quite as fast as it learns from your driving style.

Regarding lugging on hills, I let the cruise control be the boss, watching the engine temps. If they climb too much, downshift, and/or take the transmission out of 'economy' mode. The Cummins or CAT engines with the Allison transmission are really smart. Hard to hurt them.
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Old 02-14-2013, 06:39 PM   #11
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A lot of it is just "getting used to her". I remember when I got my first diesel sailboat and it seemed like it took forever to "get up to speed", when in reality, it was pushing the boat a LOT better than it's gasoline predecessor. Diesel motors seem to "build up steam" so-to-speak. Couple that with fact that your'e no longer sitting right on top of it and you'll find it's actually quite pleasant once you get used to it. A DP is on my "To Get" list.
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Old 02-14-2013, 06:50 PM   #12
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watch your boost gauge. power comes from boost. that being said you have to give it throttle to get boost. just watch your boost gauge. stock should pull to about 22 lbs., after market maybe 30lbs. then watch your exhaust temp. gauge to see how hard you're pulling your diesel. between those two gauges you'll learn pretty quick.
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Old 02-14-2013, 07:00 PM   #13
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watch your boost gauge. power comes from boost. that being said you have to give it throttle to get boost. just watch your boost gauge. stock should pull to about 22 lbs., after market maybe 30lbs. then watch your exhaust temp. gauge to see how hard you're pulling your diesel. between those two gauges you'll learn pretty quick.
Agreed, but I think most coaches don't have both of these. Even my VMSpc
only provides boost. I think adding EGT is a great idea but I haven't done it yet.

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Old 02-14-2013, 07:20 PM   #14
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If you have the Economy button turn it off for the fastest acceleration. If you want more power for the rear radiator 400 isl and have the fixed fan, change it. If you want even more getty up add the Digi Cr module and the combined two mods will give you a huge boost in acceleration and good improvement in mileage too.
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