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Horsepower vs Torque

Actually, I can make an AC motor produce max torque at zero RPM and have it decay as it speeds up or I can make it have a flat torque curve from zero RPM to base speed. It’s all done with changing parameters of the speed drive. There is so much you can do with AC speed drives that its unreal. You could even make an AC motor have the torque curve of a typical V8 if you wanted to, although that would be strange…

Imagine replacing the transmission with a generator coupled to the ICE, with an electric motor at each wheel.
Instead of gears, clutches, hydraulics and solenoid valves “gear” ratios, AWD, ABS, traction control could be implemented electronically.
Fast, smooth response; and no need to keep tire circumference closely matched.

The only issue with that would be the high unsprung weight at each wheel. You could move them inboard, back to back and have axles and cv joints to reduce the unsprung weight and still have all the other advantages.

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In my pin-head way of thinking, the torque applied to the crankshaft is directly proportional to the force on the piston from the exploding fuel… In other words you could figure it out without even having a crankshaft, just use a piston in a cylinder as a test bed, explode the fuel/air, and see how much force it produces as the piston is slammed home. The more that force is, the more torque an engine so-configured will have. So what makes that piston in a cylinder thought-experiment force greater? hmmm … well for amusement I used to put a firecracker in a water pipe and shoot a rock out of the end of the pipe as a kid, test how high it would go (Note 1). So from that experience I’d say higher torques would go with .

  • More fuel and air in the cylinder (displacement)
  • Higher compression of the fuel and air
  • It seems like for a given displacement, a wider piston and shorter stroke would yield more torque than a smaller diameter piston and longer stroke. I admit, I’m not entirely certain about that that.

Note 1: Don’t try this, it is very dangerous.

In a given engine changing the camshaft can significantly change the torque and horsepower curves. And on large domestic V-8s an RV grind will produce a much more responsive and economical engine than a performance grind. I have rebuilt a great many light truck engines and more often than not used an RV camshaft that the customers were always happy with.

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Too late, I tried it long ago back before they totally watered down the strength of firecrackers and you could still buy bottle rockets.

Long stroke and short stroke engines make about the same torque provided they have the same displacement and volumetric efficiency.
On the short stroke engine, you have more force on the connecting rod due to more piston area. On the long stroke engine, the lower force of the smaller piston works on a longer crank throw (longer lever), these two factors offset each other.
But as I have stated before, “torque” is often not meant literally, we say an engine has “torque” when what we mean is that it is extremely user friendly and pulls well at a large range of engine rpm.
One way to increase volumetric efficiency (a fancy term that means how completely the cylinder is reloaded for the next shot), is to force feed air into the engine with a blower. The only limit is what the engine can stand mechanically. Current top fuel dragsters are running about 65 psi of boost in the intake manifold and with 90% nitromethane and 10% methanol as a fuel (NHRA rule), are delivering about 7400 ft-lb or torque from a 500 CID engine. The cam lobes are even machined with an offset to compensate for crankshaft twist at full power.

Watch this on board camera shot of a top fuel dragster run and you can actually see the frame untwist a little when he shuts the engine down at the end of the run.

It’s been done. It’s called brake mean effective pressure (BMEP).

I didn’t go into that detail, but a few years ago I posted the same idea here and mentioned moving the motors inboard.

How do you think they measured the power of horses in the first place? Horses don’t make any torque, they just pull. They also don’t put out rpm, only speed.
The drawbar power formula is speed X force or distance X force / time.
To get the power in horsepower, it’s pounds of force X feet per minute divided by 33000 or pounds X feet per second divided by 550.
To get power in watts, it’s newtons of force X meters per second.

My guess, tie a horse to a wooden pallet piled with rocks. Level ground, all the same surface, gravel probably. Put some kind of calibrated spring gadget in the line between the horse and the pallet to assess the pulling force the horse requires to move the pallet. Then it’s just measuring how fast it can pull the pallet, multiply that by the force registered by the spring gadget…

Something to ponder, it seems like a team of horses, say you had 10 horses, that would be considerably more powerful than a 10 HP engine. That’s a curious thing.

James Watt standardized the power unit known as a horsepower based on how much water could be removed from coal mines by one horse per day so customers could know how big a steam engine they needed to replace the horses they were using.
It’s how much power a horse can sustain for a working day, not how much power a horse can generate during a short sprint.
A healthy human can generate one horsepower for a short sprint. A 100 pound person running up a stairway at a rate of 5.5 vertical feet per second is generating one horsepower. That’s quite doable for a short period of a few seconds.
A horse putting out maximum effort can likely put out over 20 horsepower for a brief time, i.e. just long enough to pull a stuck Model T Ford out of a ditch.

Mr Watt was right, that’s a much better way to rate the power of a horse. I guess that’s why he was a rich industrialist, and I’m not … lol …