When calculating horsepower with torque, which equation is used?

The correct equation to calculate horsepower when using torque is derived from the relationship between these two measurements and the speed of the engine in revolutions per minute (RPM). The formula Hp = (Torque x RPM) / 5252 specifically incorporates the conversion factor 5252, which is derived from the units of measurement used in the calculation.

In this equation, torque is measured in pound-feet (lb-ft) and RPM represents the engine speed. The constant 5252 comes into play because it converts the product of torque and RPM into unit horsepower. This conversion is essential because horsepower is not directly proportional to the product of torque and RPM; the number 5252 serves to normalize the calculation given the specific units of torque and speed.

Therefore, when you multiply the torque by the RPM, you effectively calculate the energy output of the engine. Dividing by 5252 gives you the horsepower, ensuring that the units remain consistent and correctly reflect the power output. This is the only equation among the choices that accurately represents this relationship, making it the correct choice for calculating horsepower based on torque and RPM.