Big Three road tests

Sport45 wrote:

buddyIam wrote:
Sports 45,

You made my point. You said it very well.

We should be concerned with power. Not horse power.

Horse power is an approximation.

It is based on torque and speed/distance. That is power that can be scientifically measured.

You don't need hp or power to have torque. But you must have torque to have power or hp.

Hp=rpm×torque/5252. The formula says it all. If there is zero rpm. Torque can be 1 million and hp would still be zero.

If hp is any number greater than zero. Then neither torque nor rpm can be zero.


Torque and rpm are the determining factors. Not hp. Hp is not a measurement it is an approximation dreamed up to sell stream engines.

Now I understand. You want to live in your own little world where you compare power by looking at a torque curve and multiplying torque and rpm. That works. The rest of us just use the HP curve where the calculations have already been made. :)

But I bet if you compare the power levels of two engines in your world you'll find the one that has 20% more power also has 20% more power in our world. Doesn't matter if you use horsepower (which you seem to dislike), elephant power, or kilowatts.

When a big RV is going down the level highway at 70 mph it is mainly the wind resistance on the vehicle that is defining the amount of torque necessary on the rear axle to maintain the vehicle speed. Slow down a bit and the torque requirement drops significantly.

When that heavy truck and trailer hit the big twisty hills things are a little different. You will likely be traveling a little slower and wind resistance is not playing nearly as big of role. The incline angle of the hill largely determines the amount of torque on the rear axle to maintain speed. If the engine isn't able to produce the necessary torque the truck slows down. Even though slowing down reduces the power required to maintain speed it makes little difference to the torque requirement which is largely being determined by the incline not wind resistance. So if the engine's torque curve is flat or falling off as the rpms drop the truck will rapidly slow down till a downshifting occurs. With this truck it is the transmission that is responsible for the torque increase. An engine (such as the Cummins) which has a significant torque rise as the rpm drops will have a higher tendency to pull the hill and downshifting will not be as often required. All this can be seen with a quick glance at an engine's torque curve.