The engine in a vehicle is the most vital and important part. The engines are made for every kind of vehicle based on a number of factors like the power that is intended to be provided to the vehicle, the weight of the vehicle, the maximum permissible weight for that vehicle, the design of the vehicle and the cost effectiveness. Keeping all the factors in mind an engine is designed and then made into the required type. The power in an engine is obtained from the piston assembly that is built inside the engine. These pistons are driven by the vehicle's fuel and the engine power is measured using horse power abbreviated as HP.