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Discussion Starter #1
If the diesel generates peak torque at low (2k) rpms, why does the truck want to rev the engine to 3500 during acceleration while towing? Won't that put it way beyond peak torque?
 

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You have your foot too far into the throttle if this is the case. I never go above 2600 rpm when towing, no need to. If you already know the diesel power is 1800-2600 rpm range ,then drive it that way.
 

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Discussion Starter #5
You have your foot too far into the throttle if this is the case. I never go above 2600 rpm when towing, no need to. If you already know the diesel power is 1800-2600 rpm range ,then drive it that way.
Well with my trailer and the terrain in my area, WOT is a frequent occurrance. Without it I would not be able to merge on the freeway or climb the hills.
 

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Well with my trailer and the terrain in my area, WOT is a frequent occurrance. Without it I would not be able to merge on the freeway or climb the hills.
You must have a heavy trailer. Mine TT. is 6140 lbs loaded for camping. We don't have freeway on Ramps to merge on around here, just hi way. But, Hills here are as steep and windy as anywhere Rockies, Cariboo, Monashee, Coquihalla, hiways are the roads we have to travel to get anywhere. I never floor my pedal, knowing my truck accelerates, and climbs much better when rolling into throttle up to 3/4 pedal or so, after that you're wasting fuel and going nowhere. Have no problem doing the speed limit, which is 90- 100 kms per hour most roads due to the steep grades and narrow roads.
If you are in a big hurry, the tendency is to floor it and get the heck moving. An inline diesel does not do well for people in a rush. It is more for driving comfortably at speed limits, easily towing a load behind without racing the engine, descending mountains with little brake input, no fuss towing.
I can see how being in a rush to get on a hi speed freeway with the little diesel could be frustrating ,mashing the pedal to the floor and getting way out of the diesel power curve by inhibiting the trans to shift up by commanding WOT . Back off a bit let it shift up, keep your foot steady at 1/2 throttle, resist pressing down more, and let the torque pull you along, you will be surprised.
Its similar to driving tractor, you won't win any drag races, but you get the job done efficiently. No drama.
 

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Discussion Starter #7
You must have a heavy trailer. Mine TT. is 6140 lbs loaded for camping. We don't have freeway on Ramps to merge on around here, just hi way. But, Hills here are as steep and windy as anywhere Rockies, Cariboo, Monashee, Coquihalla, hiways are the roads we have to travel to get anywhere. I never floor my pedal, knowing my truck accelerates, and climbs much better when rolling into throttle up to 3/4 pedal or so, after that you're wasting fuel and going nowhere. Have no problem doing the speed limit, which is 90- 100 kms per hour most roads due to the steep grades and narrow roads.
If you are in a big hurry, the tendency is to floor it and get the heck moving. An inline diesel does not do well for people in a rush. It is more for driving comfortably at speed limits, easily towing a load behind without racing the engine, descending mountains with little brake input, no fuss towing.
I can see how being in a rush to get on a hi speed freeway with the little diesel could be frustrating ,mashing the pedal to the floor and getting way out of the diesel power curve by inhibiting the trans to shift up by commanding WOT . Back off a bit let it shift up, keep your foot steady at 1/2 throttle, resist pressing down more, and let the torque pull you along, you will be surprised.
Its similar to driving tractor, you won't win any drag races, but you get the job done efficiently. No drama.
Thanks. I will give it a try. So far we have towed for only one weekend trip since the truck swap.
 

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If the diesel generates peak torque at low (2k) rpms, why does the truck want to rev the engine to 3500 during acceleration while towing? Won't that put it way beyond peak torque?
Power at the wheels is a function of engine torque and gearing. The multiplier effect of staying in a lower gear may be greater than the reduction in engine torque.

Horsepower is torque with a time element. HP = (Torque x RPM)/5252. Note that at 5252 RPM (if you can rev that high) Torque and Horsepower are always equal. Below 5252 RPM torque is always higher and above 5252 RPM Horsepower is always higher.
 

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Power at the wheels is a function of engine torque and gearing. The multiplier effect of staying in a lower gear may be greater than the reduction in engine torque.

Horsepower is torque with a time element. HP = (Torque x RPM)/5252. Note that at 5252 RPM (if you can rev that high) Torque and Horsepower are always equal. Below 5252 RPM torque is always higher and above 5252 RPM Horsepower is always higher.
Although there is that mathematical component, it doesn't really mean much because torque and HP are two different things. So being equal numbers is somewhat meaningless. To use an analogy, it would be like comparing fluid ounces to weight ounces--measuring different things.

Our engines reach peak torque at 2,000 rpm and peak HP at 3,400 rpm.


Note the the vertical axis for Torque and HP are on different sides of the graph.

Because the OP is trying to move more quickly as quickly as possible, the transmission goes to the peak HP range (but still has about 80% of the torque).

Here's an Engineering Explained simple explanation.

 

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Discussion Starter #10
Peak torque requires WOT as soon as you step on it the tranny shifts and you are off the torque curve.

Very curious.
 

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What dmaxjr said is correct. I made a notated spec sheet for you to visualize how to operate this engine efficiently while staying in the diesel powerband. I also suggest you shift in manual mode as it gives you more control over RPM and limit the agressive downshifting it does when towing with the TOW/HAUL mode engaged.

With stock tuning, the peak torque in the 2.8 is flat from 1,800-2,500 RPM. This is the ideal operating range of this engine and is shown in the blue box.

2,500 RPM is where the Peak HP and Torque occurs. Most of the torque is available until 2,500 RPM, torque begins to fall off and horsepower climbs. This is shown in the green box and arrow.

3,000 is the maximum efficient engine operation. Most of the Torque is still there @ ~ 320 lb/ft and while making ~ 170 HP. This is where the HP and TQ lines cross paths. You don't want to exceed 3,000 RPM in the 2.8. This is the red box and arrow.

 

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Try this. Turn tow haul mode OFF. Accelerate to 70 mph. Lift off the throttle. When speed drops to 60 mph, set the cruise control. The transmission will now be in 6th gear and the engine speed should now be well below 2000 rpm. You will need to repeat this after running steep hills. If your trailer is really heavy, none of this might apply.
 

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Although there is that mathematical component, it doesn't really mean much because torque and HP are two different things. So being equal numbers is somewhat meaningless. To use an analogy, it would be like comparing fluid ounces to weight ounces--measuring different things.
The only thing that moves something is force, which is torque. The only reason to move above the peak torque area is gearing which determines the actual force delivered to the rear wheels. The "thrust" for a given speed (and engine rpm) is engine torque times the transmission gearing times the differential gearing times the radius of the tire and exists without any reference to "horsepower".

Horsepower is a 17th century arbitrary definition of the work required to lift 550 lbs 1 foot in one second, which brings time into the equation. They are directly related with torque being force and horsepower being work (force with a time element). Time is included in the thrust calculation by defining the speed/engine rpm.

BTW, I am not saying the peak horsepower range is not a good place to be.
 

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What dmaxjr said is correct. I made a notated spec sheet for you to visualize how to operate this engine efficiently while staying in the diesel powerband. I also suggest you shift in manual mode as it gives you more control over RPM and limit the agressive downshifting it does when towing with the TOW/HAUL mode engaged.

With stock tuning, the peak torque in the 2.8 is flat from 1,800-2,500 RPM. This is the ideal operating range of this engine and is shown in the blue box.

2,500 RPM is where the Peak HP and Torque occurs. Most of the torque is available until 2,500 RPM, torque begins to fall off and horsepower climbs. This is shown in the green box and arrow.

3,000 is the maximum efficient engine operation. Most of the Torque is still there @ ~ 320 lb/ft and while making ~ 170 HP. This is where the HP and TQ lines cross paths. You don't want to exceed 3,000 RPM in the 2.8. This is the red box and arrow.

As I noted above, the torque and horsepower lines by definition always cross at 5,252 rpm. The chart you are looking at has a different vertical scale for torque and horsepower.
 

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As I noted above, the torque and horsepower lines by definition always cross at 5,252 rpm.
That is merely because that is the result of the definition of horsepower using foot pounds of torque. It's meaningless. They could use a different definition of horsepower and the numerical values (which again mean different things) would match at a different RPM, as they apparently do in a metric system. (See video link below.)

The 5252 is merely 33,000 (the number which defines HP) divided by 2*Pi. Pi comes into play because of the rotational function of torque and calculation of velosity. Here's an explanation of the math, and also an explanation of why it's irrelevant because torque and HP are two different measurements..

 

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Power at the wheels is a function of engine torque and gearing. The multiplier effect of staying in a lower gear may be greater than the reduction in engine torque.
This is the correct answer. All the math and graphs and videos are pretty cool, but don't really answer the question.

Remember that under drive gears multiply torque, and overdrive gears divide torque. That's why it's ideal to dyno a car in whatever gear gives you a 1:1 ratio.

I teach people to drive race cars on the road course. Coming out of a corner, I want them in the lowest gear possible, that won't hit the redline. Why? Not because the engine makes more power there, but because the lower gearing will give them maximum torque application coming out of the corner.

In Tow/Haul mode, the trans will stay in lower gears longer, and not shift in to 6th specifically to take advantage of the torque multiplication.
 

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That is merely because that is the result of the definition of horsepower using foot pounds of torque. It's meaningless. They could use a different definition of horsepower and the numerical values (which again mean different things) would match at a different RPM, as they apparently do in a metric system. (See video link below.)

The 5252 is merely 33,000 (the number which defines HP) divided by 2*Pi. Pi comes into play because of the rotational function of torque and calculation of velosity. Here's an explanation of the math, and also an explanation of why it's irrelevant because torque and HP are two different measurements..

That makes no sense. We are talking about torque and horsepower. Your math is correct though.
 

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Not because the engine makes more power there, but because the lower gearing will give them maximum torque application coming out of the corner.
Correct, the key phrase being "torque application." To be clear depending on the torque curve of the engine and gear spacing you might actually (probably?) get less torque out of the engine (despite increased horsepower) but more torque to the axle due to the lower gearing. Stated differently, the lower gear will probably give you more torque out of the transmission despite the drop in engine torque.
 
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