The physical definition of power refers to the work done by a machine in a unit of time. The amount of work is certain, and the shorter the time, the greater the power value.

The formula for calculating power is: power = force * distance / time. The common unit of force is kilograms (kg), the unit of distance is meters (m), and the unit of time is seconds (s). So the unit of power is kg.m/s. However, for the power of cars, people traditionally like to use horsepower as the unit, and the letters are PS. Manufacturers usually also give kilowatts (KW) values ​​in product descriptions.

The conversion relationship between them is as follows: 1PS=75kg.m/s=0.7355KW, 1KW=102kg.m/s=1.36PS. Maximum power is one of the most important parameters of a car engine. His size depends mainly on the size of the engine's cylinder displacement, the amount of fuel burned, and the speed of the engine. The power value is always combined with the engine speed to indicate the power delivered at this speed.

Due to the internal friction loss of the engine and the need to drive other machines, the actual effective power number is always less than the specified value. The ratio of effective power to calibrated power is called engine efficiency.

Engine power can only be measured with a professional power test stand. The working principle of the test bench is similar: the engine flywheel is connected to an electronic eddy current or water eddy current damping device via an intermediate shaft. The engine drives the damping device and its resistance can be adjusted steplessly. The "resistance moment" or "braking torque" is only indicated on the indicating instrument marked with the corresponding scale by a pull arm device, so that the power values ​​at different engine speeds are measured.

Although the test performed on the rolling test bench of the vehicle can also give the engine power value, this result is affected by the rolling resistance of the transmission, the shaft and the tire, so it can only be used as a reference value.

Different industries in the world follow different standards and test methods are also different.

The testing principle of German Industrial Standards (DIN) is: The engine is in normal operation, ie with all ancillary equipment, including intake filters and exhaust devices. Some countries, such as the United States, perform power tests in accordance with the SAE (Society of Automotive Engineers) standards. They do not include auxiliary equipment such as air filters and exhaust systems. That is, it is driven by external power. Therefore, SAE power is 15% to 20% higher than DIN. In Italy there is also a standard measurement method for CUNA. The condition is that it includes some auxiliary equipment, but does not include the air inlet filter and the exhaust device, so its power value will be 5% to 10% higher than the DIN value.

It is generally not possible to increase the power by re-calibrating the engine because modern production engines have almost all calibrated the power limit value before leaving the factory. However, if you can afford greater costs, there are some ways to increase the unit power.

The first is to increase the amount of air intake, the method is to smooth and expand the intake and exhaust channels, increase the valve cross-section of the engine, increase the compression ratio, change the valve opening and closing time, etc.; secondly, the technology of the intake and exhaust system can be debugged or even replaced. Compressor system.

All these measures intended to increase power will lead to an overall increase in engine speed levels. Therefore, advanced materials must be used to reduce the weight of moving parts while improving the machining accuracy so that they can withstand greater loads. Use stronger valve springs or even non-contact ignition systems. After this series of transformations, the power of mass-produced engines may more than double.