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Engine power is the power that an engine can put out. It can be expressed in power units, most commonly kilowatt, pferdestärke (metric horsepower), or horsepower.In terms of internal combustion engines, the engine power usually describes the rated power, which is a power output that the engine can maintain over a long period of time according to a certain testing method, for example ISO 1585.
Taxable horsepower does not reflect developed horsepower; rather, it is a calculated figure based on the engine's bore size, number of cylinders, and a (now archaic) presumption of engine efficiency. As new engines were designed with ever-increasing efficiency, it was no longer a useful measure, but was kept in use by UK regulations, which used ...
Torque is a pretty easy measurement to understand once it's explained, but horsepower can be a trickier beast. We lay out the meaning of the two ratings.
Torque forms part of the basic specification of an engine: the power output of an engine is expressed as its torque multiplied by the angular speed of the drive shaft. Internal-combustion engines produce useful torque only over a limited range of rotational speeds (typically from around 1,000–6,000 rpm for a small car).
Another means to measure torque is to connect the engine to the dynamo through a torque sensing coupling or torque transducer. A torque transducer provides an electrical signal that is proportional to the torque. With electrical absorption units, it is possible to determine torque by measuring the current drawn (or generated) by the absorber ...
The power band of an internal combustion gasoline automobile engine typically starts at midrange engine speeds (around 4,000 RPM) where maximum torque is produced, and ends below the redline after reaching maximum power (above 5,000 RPM but less than 7,000 RPM). Diesel engines in cars and small trucks may develop maximum torque below 2,000 RPM ...
Speed has dropped out of the equation, and the only variables are the torque and displacement volume. Since the range of maximum brake mean effective pressures for good engine designs is well established, we now have a displacement-independent measure of the torque-producing capacity of an engine design – a specific torque of sorts.
The useful power of an engine with shaft power output can be calculated using a dynamometer to measure torque and rotational speed, with maximum power reached when torque multiplied by rotational speed is a maximum. For jet engines the useful power is equal to the flight speed of the aircraft multiplied by the force, known as net thrust ...