Re: Z06 Reveal
Then a discussion started about torque and horsepower over on the CF. I don't think most guys understand what they are and are not, so I tried to explain it. If you ever took a basic physics course and understand the concepts of work, energy, and power you will probably understand. If not, I don't know.
At least one guy found my derivation of the Power = Torque x RPM/5252 forumula useful.
Torque is a force acting in a circle rather than a straight line. Energy is a force acting over a distance whether circular or a straight line. Power is energy per unit time, and this is what accelerates a car. A given level of power can be generated by high torque at low revs or low torque at high revs.
Power = torque acting through one revolution times number of revolutions per unit time. Say at WOT an engine produces 300 lb-ft torque at 6000 RPM. The torque is equivalent to a force acting in circle of one foot radius. So for one revolution the force travels 2pi(1) feet. (The circumference of a circle is 2pi(r).)
Power = 2pi(300)(6000) = 11,309,760 ft-lb/sec (Note the units.)
James Watt's primary customer for his new fangled steam engine in the late eighteenth century was English coal mines that used horses attached to capstans walking in a circle that drove pumps to remove water from the mines. So Watt needed to size his engine in terms of horses, and his time and motion studies indicated that a typical draft horse used to drive the pumps generated 33,000 foot-pounds of energy per minute, and he defined this power level as one horsepower.
So if we divide the 11 million plus ft-lb per minute of power above by 33,000 we get 343 horsepower.
The common formula for power with torque in lb-ft and speed in RPM, T x N/5252, comes from 2pi/33,000 = 1/5252.
Vintage electric lab dynamometers were mounted on bearings so they were free to rotate, but constrained by a lever arm of say one foot radius that rested on a scale. So the scale read torque in lb-ft and horsepower was computed by multiplying the observed torque by observed RPM at that torque reading and then usually corrected to a standard air density.
Inertia dynos like Dynojets measure power directly because it is proportional to the angular acceleration of the drum of known rotational inertia. Then by rearranging the above formula and using engine revs for N we get equivalent engine torque net of driveline/tire loss at the rear wheels.
Power is also equal to force force times velocity. If an airplane travels at 600 MPH (52,800 feet per minute) with a known engine thrust of, say 40,000 pounds, you can compute the power dissipated with proper unit conversions.
Likewise with a car at a fixed speed, if you know the total drag, which is equal to the applied thrust from the tires against the road, you can compute power.
Duke
Then a discussion started about torque and horsepower over on the CF. I don't think most guys understand what they are and are not, so I tried to explain it. If you ever took a basic physics course and understand the concepts of work, energy, and power you will probably understand. If not, I don't know.
At least one guy found my derivation of the Power = Torque x RPM/5252 forumula useful.
Torque is a force acting in a circle rather than a straight line. Energy is a force acting over a distance whether circular or a straight line. Power is energy per unit time, and this is what accelerates a car. A given level of power can be generated by high torque at low revs or low torque at high revs.
Power = torque acting through one revolution times number of revolutions per unit time. Say at WOT an engine produces 300 lb-ft torque at 6000 RPM. The torque is equivalent to a force acting in circle of one foot radius. So for one revolution the force travels 2pi(1) feet. (The circumference of a circle is 2pi(r).)
Power = 2pi(300)(6000) = 11,309,760 ft-lb/sec (Note the units.)
James Watt's primary customer for his new fangled steam engine in the late eighteenth century was English coal mines that used horses attached to capstans walking in a circle that drove pumps to remove water from the mines. So Watt needed to size his engine in terms of horses, and his time and motion studies indicated that a typical draft horse used to drive the pumps generated 33,000 foot-pounds of energy per minute, and he defined this power level as one horsepower.
So if we divide the 11 million plus ft-lb per minute of power above by 33,000 we get 343 horsepower.
The common formula for power with torque in lb-ft and speed in RPM, T x N/5252, comes from 2pi/33,000 = 1/5252.
Vintage electric lab dynamometers were mounted on bearings so they were free to rotate, but constrained by a lever arm of say one foot radius that rested on a scale. So the scale read torque in lb-ft and horsepower was computed by multiplying the observed torque by observed RPM at that torque reading and then usually corrected to a standard air density.
Inertia dynos like Dynojets measure power directly because it is proportional to the angular acceleration of the drum of known rotational inertia. Then by rearranging the above formula and using engine revs for N we get equivalent engine torque net of driveline/tire loss at the rear wheels.
Power is also equal to force force times velocity. If an airplane travels at 600 MPH (52,800 feet per minute) with a known engine thrust of, say 40,000 pounds, you can compute the power dissipated with proper unit conversions.
Likewise with a car at a fixed speed, if you know the total drag, which is equal to the applied thrust from the tires against the road, you can compute power.
Duke
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