I think torque is completely irrelevant, but everyone else will disagree with me. Power is the only thing we really care about. You can hang a 1000 lb weight on the end of a fixed beam that's 10 feet long, and you get 10000 ft-lbs of torque. But guess what, it's not moving, so there's zero power. Zero power means zero work is done, and if zero work is done, well, then nothing gets acomplished. Both power and force (torque is rotational force) are required to do work and create an energy differential.
Here's a simple example. Say you have two engines, one is gas, and one is diesel. Both engines are the same displacement, although the bores and strokes can be different. The diesel engine has a specifc torque curve which can be measured on a dyno. The gas engine is designed so that the gas engine's valve timing and ignition timing and fuel maps generate a torque curve which is *EXACTLY* the same as the diesel engine at any given shaft speed. Both engines now produce the same torque curve and the same power curve, so what's the difference? Well, the diesel engine uses alot less fuel than the gas engine, and that's the only real advantage. Maybe it can be argued that the diesel is heavier duty and will therefore last longer, but that's debatable I guess. Now, my example is never going to happen in real life, so please don't misundrestand me, it's only an example.
The reason diesels tow mow with less downshifting is because they have more low speed power and low speed torque than the typical gas engine.
To defend my statement that torque is irrelevant, I pose this argument. Drag force on airplanes, drag force on boats, drag on cars/trucks, etc, are all rated in power consumed. Some will say drag is based on a known force at a given speed, but when you have both speed and force, that's power. Look at a hydraulic system. A hydraulic pump at any given input speed produces a certain flow rate at a certain pressure. Flow is speed and pressure is force, and that's power. An electric motor requires a current and a voltage to operate. Current is the speed component, and voltage is the force component, and the two make power. Also look at a turbine engine. Say the typical fixed speed industrial turbine engine may produce 2,000 hp at 35,000 RPM. Using our forumla (available all over the internet) T=P*5252/RPM we get that the torque produced by the 2000 hp engine is only 300 ft-lbs. Doesn't sound like it will do much work, but in fact, these types of engines propel tanks and ships and trains and lots of other vehicles with ease, all that's required is gear reduction. I guess I'm getting off on a tangent so I'll stop now.
Here's a simple example. Say you have two engines, one is gas, and one is diesel. Both engines are the same displacement, although the bores and strokes can be different. The diesel engine has a specifc torque curve which can be measured on a dyno. The gas engine is designed so that the gas engine's valve timing and ignition timing and fuel maps generate a torque curve which is *EXACTLY* the same as the diesel engine at any given shaft speed. Both engines now produce the same torque curve and the same power curve, so what's the difference? Well, the diesel engine uses alot less fuel than the gas engine, and that's the only real advantage. Maybe it can be argued that the diesel is heavier duty and will therefore last longer, but that's debatable I guess. Now, my example is never going to happen in real life, so please don't misundrestand me, it's only an example.
The reason diesels tow mow with less downshifting is because they have more low speed power and low speed torque than the typical gas engine.
To defend my statement that torque is irrelevant, I pose this argument. Drag force on airplanes, drag force on boats, drag on cars/trucks, etc, are all rated in power consumed. Some will say drag is based on a known force at a given speed, but when you have both speed and force, that's power. Look at a hydraulic system. A hydraulic pump at any given input speed produces a certain flow rate at a certain pressure. Flow is speed and pressure is force, and that's power. An electric motor requires a current and a voltage to operate. Current is the speed component, and voltage is the force component, and the two make power. Also look at a turbine engine. Say the typical fixed speed industrial turbine engine may produce 2,000 hp at 35,000 RPM. Using our forumla (available all over the internet) T=P*5252/RPM we get that the torque produced by the 2000 hp engine is only 300 ft-lbs. Doesn't sound like it will do much work, but in fact, these types of engines propel tanks and ships and trains and lots of other vehicles with ease, all that's required is gear reduction. I guess I'm getting off on a tangent so I'll stop now.
