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MNBoxster · 06-15-2006, 12:00 PM

Hi,

I think there's still quite a bit of confusion here.

Horsepower = Torque * RPM / 5252

The number 5252 works only with Torque in ft-lbs. Torque measured in other units such as Newton Meters or kg-m require a different number. Visualize a one pound weight, one foot from the fulcrum on a weightless bar. Rotate that weight for one full revolution against a one pound resistance, it moved a total of 6.2832 feet (π * a two foot circle), and, incidentally, it has done 6.2832 foot pounds of work.

Now, 33,000 foot-pounds of Work/min. equals one horsepower. Divide the 6.2832 foot pounds of Work/revolution of that weight into 33,000 foot pounds, = one foot-pound of Torque at 5252 rpm or 33,000 foot pounds per minute of work, and is the equivalent of one horsepower. If we only move that weight at the rate of 2626 rpm, it's the equivalent of 1/2 horsepower (16,500 foot pounds per minute), and so on.

Maximum acceleration at any speed occurs at the HP peak.
Maximum acceleration in any gear occurs at the torque peak
Horsepower = Torque * RPM / 5252
Torque = Horsepower * 5252 / RPM
Torque = Horsepower at 5252 RPM

What is not being discussed is the Torque Curve, that is, how long an engine can operate at peak Torque throughout the RPM range.

Example: 2 Cars, each producing 300 ft. lbs. of Torque. Car #1 reaches Peak Torque at 4200 RPM and it's curve falls off at 4700 RPM. Car #2 Reaches Peak Torque at 4200 RPM but it's curve doesn't fall off until 5300 RPM. Car #2 will be faster.

Without a look at the curve, the raw numbers can be very deceiving...

Happy Motoring!... Jim'99

06-15-2006, 12:00 PM	#16
MNBoxster Registered User Join Date: Sep 2005 Location: Minneapolis/St. Paul, Minnesota, USA Posts: 3,308	Hi, I think there's still quite a bit of confusion here. Horsepower = Torque * RPM / 5252 The number 5252 works only with Torque in ft-lbs. Torque measured in other units such as Newton Meters or kg-m require a different number. Visualize a one pound weight, one foot from the fulcrum on a weightless bar. Rotate that weight for one full revolution against a one pound resistance, it moved a total of 6.2832 feet (π * a two foot circle), and, incidentally, it has done 6.2832 foot pounds of work. Now, 33,000 foot-pounds of Work/min. equals one horsepower. Divide the 6.2832 foot pounds of Work/revolution of that weight into 33,000 foot pounds, = one foot-pound of Torque at 5252 rpm or 33,000 foot pounds per minute of work, and is the equivalent of one horsepower. If we only move that weight at the rate of 2626 rpm, it's the equivalent of 1/2 horsepower (16,500 foot pounds per minute), and so on. Maximum acceleration at any speed occurs at the HP peak. Maximum acceleration in any gear occurs at the torque peak Horsepower = Torque * RPM / 5252 Torque = Horsepower * 5252 / RPM Torque = Horsepower at 5252 RPM What is not being discussed is the Torque Curve, that is, how long an engine can operate at peak Torque throughout the RPM range. Example: 2 Cars, each producing 300 ft. lbs. of Torque. Car #1 reaches Peak Torque at 4200 RPM and it's curve falls off at 4700 RPM. Car #2 Reaches Peak Torque at 4200 RPM but it's curve doesn't fall off until 5300 RPM. Car #2 will be faster. Without a look at the curve, the raw numbers can be very deceiving... Happy Motoring!... Jim'99 Last edited by MNBoxster; 06-15-2006 at 12:21 PM.