The engine is one of the most important components of your racer. Since a copter generates thrust and lift only through the engines, they are crucial to the power of your copter. For 5 inch FPV-Racing Copters motors between 2204 to 2407 with 2000 kV to 2800 kV are used. The number combination describes the stator diameter (22xx = 22mm diameter) and the stator height (xx07 = 7mm height). The larger the values, the more power and torque the motor has and can turn larger propellers - but it is also heavier. The kV number indicates the nominal speed of the motor, here also applies: the higher the value, the more power the motor has. However, the speed must be adjusted to the propeller.
Therefore the engines should be selected together with the ESCs and the propellers to find a good balance between power and efficiency.