Hp v Torque
11-03-2004, 10:56 PM
#33
5th Gear Member
Join Date: Mar 2004
Location:
Posts: 4,813
RE: Hp v Torque
torque is a measurement of FORCE, measured in ft-lb., and is the end result of a force being applied to a lever arm in order to twist something. in an internal combustion engine, the applied force is the pushing down on the piston by the combustion of the fuel/air mixture in the cylinder that pushes down onto the rod which is attached off center to a crankshaft which converts the straight line force into a rotary motion. the longer the stroke, the more torque is produced for the same combustion pressure as the lever arm on the crankshaft is longer with a longer stroke versus a shorter stroke.
horsepower is a measurement of WORK done over time. in the case of an piston driven engine, by the application of a torque force onto a crankshaft at a given engine speed. work requires the motion of some mass over some period of time.
the previous given formula for calculating horsepower requires you to know two variables, the torque being applied and the speed of the crankshaft which supplies the time factor needed to calculate work being done.
HP = (torque x rpm)/5252 the 5252 is a correction factor that changes the result in units of HP. (since HP is a derivative of torque, the two curves will always cross each other at 5525 rpm.)
engine or chassis dynomometers measure the TORQUE being produced by the engine and calculate the HP or work being done.
you can apply torque all day long without doing any "work" unless there is motion involved! (look at using a torque wrench to measure the tightness of a head bolt, you apply a torsional force to the bolt but do no real "work" as no mass is moved any distance over time.)
now that we have defined the terms correctly, let's review what the relationship is between the two.
TORQUE is what gets things in motion and keeps them in motion. HORSEPOWER is the amount of work being done during the motion.
in the case of a car, you have to do "work" to overcome the forces of friction between the tires and the road surface and to overcome the resistance of the air on the various surfaces of the car as it moves through the air. once the car is in motion, it takes less torque to keep it moving than it did to get it moving (law of inertia: bodies at rest tend to stay at rest, bodies in motion tend to stay in motion) until the speed of the car begins to meet the friction of moving through the air. for this reason, cars use transmissions and rear differential gears to multiply the engine torque at low engine speeds to get the car into motion without stalling the engine. ever see a sprint car, the driveshaft is welded to the engine flywheel. it has to be pushed to get it started since it has no transmission and is "in gear" all the time and therefore no way for the engine to produce any torque at rest, it has to be turning first by being pushed and then the engine can be started and run making torque. once in motion, the engine makes sufficient torque to keep the car in motion until it comes to rest again at which point the engine stalls and stops.
transmissions use lower gears (higher numerical ratios) in order to multiply the torque being produced by the engine at relatively low engine speeds to get the car moving in a smooth manner. once in motion, the gears become higher ones (lower numerical ratios) until the engine and the tranny output shaft are in high gear, or 1:1 ratio, meaning they are turning at the same speed.
for the car to move, the engine must accelerate the car down the road and through the air. since Force = mass x acceleration, the engine TORQUE is the FORCE which provides for the acceleration of the car from rest and into motion.
once in motion, the air resistance to the movement increases with the square of the vehicle speed, meaning that as the speed doubles, the air resistance forces go up by a factor of 4 times. this is where the HORSEPOWER comes into play, it takes large amounts of horsepower to increase the speed of the vehicle and to overcome the forces of rolling resistance and air resistance to the motion of the car.
but it all gets into motion because the engine makes sufficient torque to overcome all the other forces at work trying to keep the car from moving. [sm=exactly.gif]
horsepower is a measurement of WORK done over time. in the case of an piston driven engine, by the application of a torque force onto a crankshaft at a given engine speed. work requires the motion of some mass over some period of time.
the previous given formula for calculating horsepower requires you to know two variables, the torque being applied and the speed of the crankshaft which supplies the time factor needed to calculate work being done.
HP = (torque x rpm)/5252 the 5252 is a correction factor that changes the result in units of HP. (since HP is a derivative of torque, the two curves will always cross each other at 5525 rpm.)
engine or chassis dynomometers measure the TORQUE being produced by the engine and calculate the HP or work being done.
you can apply torque all day long without doing any "work" unless there is motion involved! (look at using a torque wrench to measure the tightness of a head bolt, you apply a torsional force to the bolt but do no real "work" as no mass is moved any distance over time.)
now that we have defined the terms correctly, let's review what the relationship is between the two.
TORQUE is what gets things in motion and keeps them in motion. HORSEPOWER is the amount of work being done during the motion.
in the case of a car, you have to do "work" to overcome the forces of friction between the tires and the road surface and to overcome the resistance of the air on the various surfaces of the car as it moves through the air. once the car is in motion, it takes less torque to keep it moving than it did to get it moving (law of inertia: bodies at rest tend to stay at rest, bodies in motion tend to stay in motion) until the speed of the car begins to meet the friction of moving through the air. for this reason, cars use transmissions and rear differential gears to multiply the engine torque at low engine speeds to get the car into motion without stalling the engine. ever see a sprint car, the driveshaft is welded to the engine flywheel. it has to be pushed to get it started since it has no transmission and is "in gear" all the time and therefore no way for the engine to produce any torque at rest, it has to be turning first by being pushed and then the engine can be started and run making torque. once in motion, the engine makes sufficient torque to keep the car in motion until it comes to rest again at which point the engine stalls and stops.
transmissions use lower gears (higher numerical ratios) in order to multiply the torque being produced by the engine at relatively low engine speeds to get the car moving in a smooth manner. once in motion, the gears become higher ones (lower numerical ratios) until the engine and the tranny output shaft are in high gear, or 1:1 ratio, meaning they are turning at the same speed.
for the car to move, the engine must accelerate the car down the road and through the air. since Force = mass x acceleration, the engine TORQUE is the FORCE which provides for the acceleration of the car from rest and into motion.
once in motion, the air resistance to the movement increases with the square of the vehicle speed, meaning that as the speed doubles, the air resistance forces go up by a factor of 4 times. this is where the HORSEPOWER comes into play, it takes large amounts of horsepower to increase the speed of the vehicle and to overcome the forces of rolling resistance and air resistance to the motion of the car.
but it all gets into motion because the engine makes sufficient torque to overcome all the other forces at work trying to keep the car from moving. [sm=exactly.gif]
11-03-2004, 11:08 PM
#34
2nd Gear Member
Join Date: Jul 2004
Location:
Posts: 355
RE: Hp v Torque
ORIGINAL: roundman
torque is a measurement of FORCE, measured in ft-lb., and is the end result of a force being applied to a lever arm in order to twist something. in an internal combustion engine, the applied force is the pushing down on the piston by the combustion of the fuel/air mixture in the cylinder that pushes down onto the rod which is attached off center to a crankshaft which converts the straight line force into a rotary motion. the longer the stroke, the more torque is produced for the same combustion pressure as the lever arm on the crankshaft is longer with a longer stroke versus a shorter stroke.
horsepower is a measurement of WORK done over time. in the case of an piston driven engine, by the application of a torque force onto a crankshaft at a given engine speed. work requires the motion of some mass over some period of time.
the previous given formula for calculating horsepower requires you to know two variables, the torque being applied and the speed of the crankshaft which supplies the time factor needed to calculate work being done.
HP = (torque x rpm)/5252 the 5252 is a correction factor that changes the result in units of HP. (since HP is a derivative of torque, the two curves will always cross each other at 5525 rpm.)
engine or chassis dynomometers measure the TORQUE being produced by the engine and calculate the HP or work being done.
you can apply torque all day long without doing any "work" unless there is motion involved! (look at using a torque wrench to measure the tightness of a head bolt, you apply a torsional force to the bolt but do no real "work" as no mass is moved any distance over time.)
now that we have defined the terms correctly, let's review what the relationship is between the two.
TORQUE is what gets things in motion and keeps them in motion. HORSEPOWER is the amount of work being done during the motion.
in the case of a car, you have to do "work" to overcome the forces of friction between the tires and the road surface and to overcome the resistance of the air on the various surfaces of the car as it moves through the air. once the car is in motion, it takes less torque to keep it moving than it did to get it moving (law of inertia: bodies at rest tend to stay at rest, bodies in motion tend to stay in motion) until the speed of the car begins to meet the friction of moving through the air. for this reason, cars use transmissions and rear differential gears to multiply the engine torque at low engine speeds to get the car into motion without stalling the engine. ever see a sprint car, the driveshaft is welded to the engine flywheel. it has to be pushed to get it started since it has no transmission and is "in gear" all the time and therefore no way for the engine to produce any torque at rest, it has to be turning first by being pushed and then the engine can be started and run making torque. once in motion, the engine makes sufficient torque to keep the car in motion until it comes to rest again at which point the engine stalls and stops.
transmissions use lower gears (higher numerical ratios) in order to multiply the torque being produced by the engine at relatively low engine speeds to get the car moving in a smooth manner. once in motion, the gears become higher ones (lower numerical ratios) until the engine and the tranny output shaft are in high gear, or 1:1 ratio, meaning they are turning at the same speed.
for the car to move, the engine must accelerate the car down the road and through the air. since Force = mass x acceleration, the engine TORQUE is the FORCE which provides for the acceleration of the car from rest and into motion.
once in motion, the air resistance to the movement increases with the square of the vehicle speed, meaning that as the speed doubles, the air resistance forces go up by a factor of 4 times. this is where the HORSEPOWER comes into play, it takes large amounts of horsepower to increase the speed of the vehicle and to overcome the forces of rolling resistance and air resistance to the motion of the car.
but it all gets into motion because the engine makes sufficient torque to overcome all the other forces at work trying to keep the car from moving. [sm=exactly.gif]
torque is a measurement of FORCE, measured in ft-lb., and is the end result of a force being applied to a lever arm in order to twist something. in an internal combustion engine, the applied force is the pushing down on the piston by the combustion of the fuel/air mixture in the cylinder that pushes down onto the rod which is attached off center to a crankshaft which converts the straight line force into a rotary motion. the longer the stroke, the more torque is produced for the same combustion pressure as the lever arm on the crankshaft is longer with a longer stroke versus a shorter stroke.
horsepower is a measurement of WORK done over time. in the case of an piston driven engine, by the application of a torque force onto a crankshaft at a given engine speed. work requires the motion of some mass over some period of time.
the previous given formula for calculating horsepower requires you to know two variables, the torque being applied and the speed of the crankshaft which supplies the time factor needed to calculate work being done.
HP = (torque x rpm)/5252 the 5252 is a correction factor that changes the result in units of HP. (since HP is a derivative of torque, the two curves will always cross each other at 5525 rpm.)
engine or chassis dynomometers measure the TORQUE being produced by the engine and calculate the HP or work being done.
you can apply torque all day long without doing any "work" unless there is motion involved! (look at using a torque wrench to measure the tightness of a head bolt, you apply a torsional force to the bolt but do no real "work" as no mass is moved any distance over time.)
now that we have defined the terms correctly, let's review what the relationship is between the two.
TORQUE is what gets things in motion and keeps them in motion. HORSEPOWER is the amount of work being done during the motion.
in the case of a car, you have to do "work" to overcome the forces of friction between the tires and the road surface and to overcome the resistance of the air on the various surfaces of the car as it moves through the air. once the car is in motion, it takes less torque to keep it moving than it did to get it moving (law of inertia: bodies at rest tend to stay at rest, bodies in motion tend to stay in motion) until the speed of the car begins to meet the friction of moving through the air. for this reason, cars use transmissions and rear differential gears to multiply the engine torque at low engine speeds to get the car into motion without stalling the engine. ever see a sprint car, the driveshaft is welded to the engine flywheel. it has to be pushed to get it started since it has no transmission and is "in gear" all the time and therefore no way for the engine to produce any torque at rest, it has to be turning first by being pushed and then the engine can be started and run making torque. once in motion, the engine makes sufficient torque to keep the car in motion until it comes to rest again at which point the engine stalls and stops.
transmissions use lower gears (higher numerical ratios) in order to multiply the torque being produced by the engine at relatively low engine speeds to get the car moving in a smooth manner. once in motion, the gears become higher ones (lower numerical ratios) until the engine and the tranny output shaft are in high gear, or 1:1 ratio, meaning they are turning at the same speed.
for the car to move, the engine must accelerate the car down the road and through the air. since Force = mass x acceleration, the engine TORQUE is the FORCE which provides for the acceleration of the car from rest and into motion.
once in motion, the air resistance to the movement increases with the square of the vehicle speed, meaning that as the speed doubles, the air resistance forces go up by a factor of 4 times. this is where the HORSEPOWER comes into play, it takes large amounts of horsepower to increase the speed of the vehicle and to overcome the forces of rolling resistance and air resistance to the motion of the car.
but it all gets into motion because the engine makes sufficient torque to overcome all the other forces at work trying to keep the car from moving. [sm=exactly.gif]
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