How to Calculate Power to Weight Ratios in Automobiles
A vehicle's ability to reach a given distance at a specified time depends on the vehicle's weight and its power. "Power" is defined as either the amount of horsepower the engine produces, or the amount of torque produced. If the engine's power output is increased and the vehicle's weight is the same, the vehicle will be quicker. If the engine's power is constant but the vehicle's weight is reduced, the vehicle will also be quicker. The converse of these principals is also true.
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Instructions
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Measure the weight of the vehicle. Many truck-stop scales will weigh the vehicle, as will some large recycling facilities. These recycling facilities typically weigh a vehicle with the recycled materials still loaded onto the vehicle, then weigh the vehicle once the materials have been unloaded to determine the weight of the recycled material. Talk to the manager of the recycling plant to find out if the vehicle can be weighed by itself.
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Measure the engine's power output using a dynometer. A dynometer is an instrument which measures both the torque and horsepower produced by an engine. It also specifies at which RPMs the engine produces the maximum amount of power. The automobile is actually driven onto the dynometer, which allows the rear wheels to spin while the automobile stays stationary. Dynometers are extremely expensive instruments to purchase. However, most race-engine modification shops have dynometers and can test your automobile's power output for you.
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Divide the total weight of the vehicle by the engine's horsepower to calculate the engine's horsepower-to-weight ratio. For example, if a 2,800-lb. vehicle produces 300 horsepower, the power-to-weight ratio is 1 horsepower for every 9.33 lbs. To calculate the engine's torque-to-weight ratio, simply substitute the horsepower figure with the torque figure.
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