Understanding power vs torque on a dynometer
Posted: 20 Jul 2018 10:27
In Carlo’s thread I stated that torque cannot be measured on a dyno.
In essence the statement is correct.
The dyno employs a load-cell to measure torque as it is impossible to measure torque at the rollers.
"Do you want your engine to make HORSEPOWER or TORQUE?"
This question is usually asked in a tone which strongly suggests that "experts" believe power and torque are somehow mutually exclusive.
In fact, the opposite is true, and you should be clear on these facts:
POWER (the rate of doing WORK) is dependent on TORQUE and RPM.
TORQUE and RPM are the MEASURED quantities of engine output.
POWER is CALCULATED from torque and RPM, by the following equation
HP = Torque x RPM ÷ 5252
An interesting fun fact is because of the mathematical constant
All vehicles, no matter which, will therefor produce their same torque figure and power figure at 5252 RPM.
Get your head around that!
An engine produces POWER by providing a ROTATING SHAFT which can exert a given amount of TORQUE on a load at a given RPM. The amount of TORQUE the engine can exert usually varies with RPM.
So using the sketch below with respect to an engine
The simplest explanation is thus
Torque is the tangential force to turn the shaft
That shafts ability to drive something else is the power
And that’s why the dyno measure the power rather than anything else.
In essence the statement is correct.
The dyno employs a load-cell to measure torque as it is impossible to measure torque at the rollers.
"Do you want your engine to make HORSEPOWER or TORQUE?"
This question is usually asked in a tone which strongly suggests that "experts" believe power and torque are somehow mutually exclusive.
In fact, the opposite is true, and you should be clear on these facts:
POWER (the rate of doing WORK) is dependent on TORQUE and RPM.
TORQUE and RPM are the MEASURED quantities of engine output.
POWER is CALCULATED from torque and RPM, by the following equation
HP = Torque x RPM ÷ 5252
An interesting fun fact is because of the mathematical constant
All vehicles, no matter which, will therefor produce their same torque figure and power figure at 5252 RPM.
Get your head around that!
An engine produces POWER by providing a ROTATING SHAFT which can exert a given amount of TORQUE on a load at a given RPM. The amount of TORQUE the engine can exert usually varies with RPM.
So using the sketch below with respect to an engine
The simplest explanation is thus
Torque is the tangential force to turn the shaft
That shafts ability to drive something else is the power
And that’s why the dyno measure the power rather than anything else.