Horsepower is actually an older measurement for power its origins came from a time when most heavy work and lifting were done literally through horses. With the arrival of the steam engine, the power or capacity of the engine to do work within a given period of time was still measured in terms comparable to what horses can do given the same amount of load to work with.
- Use the ET (elapsed time) method. This method computes your car's engine horsepower based on its weight and the time it took to travel one quarter of a mile or 1,330 feet. The formula is stated thus: horsepower = weight / (elapsed time/5.825)3. When determining the car's weight, remember to include your weight and use pounds for measurement units to be consistent. Furthermore, use a stop watch to measure the elapsed time. You might need an assistant to handle the stop watch and record the elapsed time - be sure to include his or her weight too.
- Use the trap speed method. This technique on the other hand determines horsepower based on the weight and the speed of the car after traveling one quarter of a mile. The formula this time is: horsepower = weight x (speed/234) 3. As with the ET method add driver and passenger weight to the car's weight. For speed use miles-per-hour units to maintain consistency.
- Make use of a chassis dynamometer. Among the many types of horsepower measurements that can be applied to automotive vehicles, true horsepower or wheel horsepower is the one that indicates forward movement. This type of horsepower is accurately measured through a device known as a chassis dynamometer. The car is mounted on rollers and the engine is run. The car engine's operation turns these rollers and attached monitoring equipment measures the power output in horsepower units.
There are actually various types of horsepower depending on the type of work or engine that is being measured. To accurately measure horsepower and make the quantity meaningful, one has to take into consideration the context, use the correct formula, and qualify what is actually measured. The most basic form of horsepower is mechanical horsepower and this is defined accordingly as the load being carried (in pounds) multiplied by the rate of movement (feet per minute), divided by 33,000 pounds. One horsepower therefore is the amount of power needed to move 33,000 pounds a distance of 1 foot in 1 minute. The current equivalent for horsepower in the established International System of Units is "watt." Based on the formula for computing mechanical horsepower, 1 horsepower is equivalent to 746 watts.