The present paper provides a mathematical dynamic modelling and analysis of a newly developed electrical power supply system for petrol cars. The main goal of this research work is to improve the economic operation of the car’s electric power supply aiming at fuel economy improvement and for less gases emission. The proposed scheme has been studied and investigated using MATLAB/SIMULINK(R) toolbox and C language. The dynamic behaviour of the proposed system has been analysed for two different driving cycles and the results showed a fuel economy improvement in the investigated two cases. It is shown that the proposed approach is very superior to the conventional one, which is widely used in most of public cars. However, it also shows very encouraging results in terms of fuel save and less gas emission. The main advantage of the method proposed is its applicability to any first or second hand low cost cars.