Cat vs Powerstroke torque curves

ShinerBock wrote:

4x4ord wrote:

The principle is this:
Think about power as the rate of doing work. Think of a shaft with a cable wrapped around it. Attached to the other end of the cable is a weight. The cable and weight create a force on the shaft referred to as torque. As the shaft rotates the cable is wound and the weight is lifted. In order to turn the shaft fast with a light weight a certain amount of power is required. Now if the shaft is turned half as fast and the weight is twice as heavy the exact same amount of power is required.

A couple of trucks pulling identical trailers up a hill both have rear axles. If both trucks have the same size tires and are traveling the same speed they will have the exact same torque on there rear axles. If the tow trucks are travelling the same speed there axles will be turning the same speed. The rear axles on both trucks will be transmitting the exact same amount of power. Now look at what is driving those axles. If one engine is turning 5 times as fast as the trucks rear axle it will have a torque of 1/5 the axle torque on its crankshaft. That engine is delivering the exact same horsepower as the rear axle. If the other engine is turning 7 times as fast as the axle it will have a torque on its crankshaft which is 1/7 the rear axle torque and it will be transmitting the same power as the rear axle.

I think the thing that gets people arguing is that high torque engines tend to have flatter power curves. With a flat power curve the engine is actually able to put close to its rated power to the axle over a wider rpm range. If infinite variable speed transmissions were coupled to engines the higher peak horsepower engine would always be able to out pull the lower horsepower engine.

I completely understand how engines work along with how horsepower and torque works. I am just saying that the article stating that torque is not important in a towing engine or when pulling heavy weight up hills is completely and utterly false. You need both horsepower and torque. There are actually formulas of how much torque is needed to move certain weight and overcome x amount of force.

Also, in his examples of an engine with less horsepower and more torque versus one with more horsepower and less torque, he is using gearing to multiply the torque of the engine with less torque. Without that gearing to multiply the torque, the engine with the less torque would not be able to pull the amount of weight the higher torque engine could if all things like gearing were equal.

Like my example earlier with the Ram 2500 6.4L Hemi and 6.7L diesel that have the exact same trans gearing, but with the Hemi having slightly shorter rear gears. Unloaded or with a light load, the Hemi should run circles around the Cummins due the Hemi having more horsepower. As you add more weight to the equation and more torque is need to overcome the force needed(i.e.inclines) to keep the wheels turning, then the higher torque of the Cummins will overcome the Hemi even though the Cummins has a narrower rpm range.

This is why I say I don't completely agree with the article because torque (and horsepower) is needed whether it is through gearing or in the engine. All the horsepower (work) in the world is useless if you don't have enough torque to turn the crank and keep it moving to make power.

I think you'll have a hard time finding a false statement in that article, but I also agree with you that if a high horsepower engine is not geared properly it wont be able to put enough torque to the rear axle to make use of its power.