It is sad but true when it comes to engines, they don’t manufacture them similarly. The user manual and official literature might state that your car’s engine produces, let’s say, 100 kW. Well, they just round that figure off from the average that they obtain from other similar engines. Very few of these engine types will develop exactly 100 kW. The reason is that engines are mechanical devices that consist of hundreds of parts. These parts all have to fit together well to make it work. The constraints of economical mass production mean that manufacturers allow a certain tolerance range for the parts it manufactures. That means that these parts have to be of certain dimensions within an accepted range of variance. It would simply be too expensive – and virtually impossible – to mass-manufacture engines to such fine tolerances that they are identical.