Much like full-sized motorcycle engines, pit bike engines are measured in cc, or cubic centimeters. This number refers to how much displacement one of the cylinders can cause, or how much air and fuel the cylinder can push through the engine when it revolves one time. The smaller the number, the less powerful the pit bike engines will be. Pit bike engines generally range from about 25cc to 100cc, though other sizes do exist depending on the owner's needs. Since pit bikes are generally used for navigating the pit areas of motorcycle races, the engines do not have to be very powerful, but since their inception, pit bikes have also been used for racing purposes, necessitating more powerful engines.
Most pit bike engines are two stroke engines. This means a piston revolves two times during combustion rather than four times. A two stroke engine is generally more powerful than a four stroke engine, but it also burns through fuel more quickly and will cause more wasted exhaust. Most smaller engines such as lawnmower engines or chainsaw engines are two stroke, and pit bike engines are no different. Using a two stroke engine instead of a four stroke engine means more power in a smaller engine, and less manufacturing costs since less materials and technology are necessary to make a two stroke engine work.
Some pit bike engines are not gasoline-powered at all. Early racing versions of the engines were electric, powered by batteries large enough to allow the engine to run for an extended period of time. These types of engines have generally become antiquated, since gas-powered engines are more powerful and more convenient to run. Electric engines need to be charged, which means an electrical source is necessary, while gas-powered engines do not need to be charged and can be refueled easily with gas stored in a portable gas can.
Some racers will put more powerful engines in their pit bikes. It is not unheard of to install a 200cc engine on a pit bike, though such engines are powerful enough to propel the tiny bike at high speeds, meaning proper safety precautions should be taken. For smaller individuals such as children, a 25 to 50cc engine is sufficient to drive the motorcycle at moderate speeds. Heavier pit bikes, such as those that imitate chopper bikes, may be heavy enough that a larger engine is necessary to drive it properly, though in most recreational applications, a small to medium sized pit bike engine is sufficient.