Unfortunately the laws of physics deem perpetual motion impossible. You cannot get more energy out then you put in all you can do is change the form of energy. Now with your example with a good electric motor attached via a low loss gear system to a dynamo, You would be able to see that if you put 100kw into the motor you only get about 90KW out of the dynamo. That is of course assuming that you could get the system to work. However what you can do with this type of system is cut your losses. For example if you put 100kw of energy into the electric motor and used that to drive a wheel what you could do is that when only 50kw are needed (when it is up to speed) then you can save about 49 of the 50 left over KW of energy to use later!
Power, whether measured as HP, PS, or KW is what accelerates cars and gets it up to top speed. Power also determines how far you take a wall when you hit it
Engine torque is an illusion.