Horsepower and Torque
03-08-2005, 12:07 PM
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Originally Posted by dcak,Mar 8 2005, 12:46 PM
Without reading 4 pages of thread, this statement couldn't be more wrong. Helicopters use gas turbines to turn their rotors. And torque is what turnes em.
Replace "gas turbines" with "rocket engines" and you'll get what I was actually trying to say.
03-08-2005, 05:23 PM
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Originally Posted by Zoran,Mar 8 2005, 11:44 AM
Look guys, it's really quite simple.
Acceleration is work. Horsepower is a measure of the ability to perform work. Therefore, horsepower is the measure of the ability to accelerate. End of story.
How do you generate energy to perform that work is your problem. Internal combustion engines use fuel burning in cylinders to generate force that turns the crankshaft. Rocket engines use thrust. Bicycles use your muscles. It doesn't matter.
The only thing that matters is the ABILITY to accelerate. And that's measured by horsepower.
People get so hung up on torque because they don't really understand the physics. Yes, there is torque generated in the IC engines, and yes it is important but not because it accelerates your car but because most cars have gears and the shape of the torque curve (or horsepower curve) is important. If all cars had CVT's nobody would even mention torque.
Torque doesn't accelerate your car. The chemical energy of the fuel being burnt in your engine accelerates your car.
Torque is not a measure in any way of your car's ability to accelerate. Horserpower is.
Torque doesn't get you off the line. Horsepower at your launch RPM and your traction do.
Torque doesn't tow trailers. Horsepower does. It's just that an engine making that HP with more torque and less RPM will last a lot longer towing trailers than an engine making that HP with less torque and more RPM.
Last but not least: I make about 200 lb-ft of torque with my legs on my bicycle. Does that mean I can in any imaginable way beat a guy on a Hayabusa with his "measly" 100 lb-ft of torque, even though I'm A LOT lighter? Will I beat him off the line? Will I beat him from a roll? Will I beat him up the hill? Will I beat him if we both tow a 500 lbs trailer behind us?
Think about it.
Acceleration is work. Horsepower is a measure of the ability to perform work. Therefore, horsepower is the measure of the ability to accelerate. End of story.
How do you generate energy to perform that work is your problem. Internal combustion engines use fuel burning in cylinders to generate force that turns the crankshaft. Rocket engines use thrust. Bicycles use your muscles. It doesn't matter.
The only thing that matters is the ABILITY to accelerate. And that's measured by horsepower.
People get so hung up on torque because they don't really understand the physics. Yes, there is torque generated in the IC engines, and yes it is important but not because it accelerates your car but because most cars have gears and the shape of the torque curve (or horsepower curve) is important. If all cars had CVT's nobody would even mention torque.
Torque doesn't accelerate your car. The chemical energy of the fuel being burnt in your engine accelerates your car.
Torque is not a measure in any way of your car's ability to accelerate. Horserpower is.
Torque doesn't get you off the line. Horsepower at your launch RPM and your traction do.
Torque doesn't tow trailers. Horsepower does. It's just that an engine making that HP with more torque and less RPM will last a lot longer towing trailers than an engine making that HP with less torque and more RPM.
Last but not least: I make about 200 lb-ft of torque with my legs on my bicycle. Does that mean I can in any imaginable way beat a guy on a Hayabusa with his "measly" 100 lb-ft of torque, even though I'm A LOT lighter? Will I beat him off the line? Will I beat him from a roll? Will I beat him up the hill? Will I beat him if we both tow a 500 lbs trailer behind us?
Think about it.
We're agreeing in that HP is a "measurement" of the ability to perform work!!!
I think that's where we're getting hung up. HP is a measurement of the ability to do work and as such is a great predictor of the kind of performance one can expect from a given vehicle.
HP isn't "DOING" the work. It's a measurement "OF" the "WORK PERFORMED!"
You are right in that the energy for all of this comes from the "chemical energy of fuel being burnt" but that energy is:
1. pushing a piston downward in a cylinder.
2. which is then turning a crankshaft through a connecting rod.
3. and that "force" generated on that crankshaft that causes it to turn, IS TORQUE!
THAT is what's turning the crankshaft and subsequently the transmission were it is multiplied through the gears to ultimately turn the drive shaft and wheels that then makes the car move. They then measure how fast all of this happens and calculate the HP produced!
To say that torque has nothing to do with the cars ability to accelerate is ludicrous. How much "torque" the engine can make at how high an rpm is directly related to how much of your precious HP the engine can produce. The two are inseparably tied together.
What you're performance on bicycle compared to the performance of a Hayabusa (the fastest stock production motorcycle in the world as far as I know, for those who may not have known) has to do with all of this I don't know. How fast can you pedal that bicycle at 200 ft/lbs vs how fast is the Busa's engine turning to produce it's 100 ft/lbs is all the difference. Sure the Busa will be making a LOT more HP than you will be but my point in all of this is that neither of you will be making any HP until that TORQUE is applied and work is actually performed. Then and only then can you make a "measurement" of what actually happened!
You can try to divert the discussion with examples of jets and turbines but that's not what we're talking about. It's apples and oranges. We're talking about cars and reciprocating piston engines and a very simple equation that says "torque x rpm / 5252 = HP"
You can't have HP without torque, in this case! and until that torque is applied, you're not going anywhere!
Drive Safe,
Steve R.
03-09-2005, 06:04 AM
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In the process of converting the chemical energy of the gasoline into acceleration there's a WHOLE LOT OF THINGS going on.
There's the force pushing the piston down.
There's the engine torque turning the crankshaft.
There are the gears multiplying the engine torque and generating driveshaft torque.
There is the driveshaft connecting the gearbox and the differential.
There is the differential converting the driveshaft torque into rear wheel torque.
There are the wheels turning wheel torque into forward thrust.
ALL of these things are equally important, but for some reason a lot of people just choose to pick the engine torque as somehow "most important" and the one accelerating the car.
If one was to say "gearbox is the one accelerating the car, everything else is just calculated" one would be laughed at. Yet such a thing does not happen when an equally simplistic and naive statement "engine torque is the one accelerating the car" is made.
The only things that matter are the beginning and the end. From some source of energy to forward thrust. The only thing describing that is horsepower.
There's the force pushing the piston down.
There's the engine torque turning the crankshaft.
There are the gears multiplying the engine torque and generating driveshaft torque.
There is the driveshaft connecting the gearbox and the differential.
There is the differential converting the driveshaft torque into rear wheel torque.
There are the wheels turning wheel torque into forward thrust.
ALL of these things are equally important, but for some reason a lot of people just choose to pick the engine torque as somehow "most important" and the one accelerating the car.
If one was to say "gearbox is the one accelerating the car, everything else is just calculated" one would be laughed at. Yet such a thing does not happen when an equally simplistic and naive statement "engine torque is the one accelerating the car" is made.
The only things that matter are the beginning and the end. From some source of energy to forward thrust. The only thing describing that is horsepower.
03-09-2005, 06:12 AM
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BTW, I'm done here.
People can choose to believe what they want and get hung up on what they want. I'm not about to engage in a quest to change that.
Getting hung up on engine torque is (to me) equally silly as getting hung up, for example, on piston rod length.
"My torque is 200 lb-ft and yours is 150 lb-ft so I'll get you off the line" is equally stupid as "My piston rod is 10 inches and yours is 8 inches, so I'll get you off the line". In both cases you're picking just one variable in the equation and ignoring everything else.
People can choose to believe what they want and get hung up on what they want. I'm not about to engage in a quest to change that.
Getting hung up on engine torque is (to me) equally silly as getting hung up, for example, on piston rod length.
"My torque is 200 lb-ft and yours is 150 lb-ft so I'll get you off the line" is equally stupid as "My piston rod is 10 inches and yours is 8 inches, so I'll get you off the line". In both cases you're picking just one variable in the equation and ignoring everything else.
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