How in the hell could a 100% efficient engine be built?

okay so there has never in the history of humanity been a 100% efficient engine of any sort. electric is quite efficient, but not perfect because of electrical resistance in the wires that make the machine. gasoline is only about 30% efficient due to heat loss and inefficient/incomplete destruction of the hydrocarbon molecules that make octane, not to mention impurities in gasoline. a bicycle is only about 16% efficient, and a body is probably the most inefficient because of heat loss and personal motivation even though approximately 90% of food energy is used. so if a perfect machine were to be, would it be a reptilian cold blooded engine? but then it would need external heating. if it were a solar powered green machine it wouldnt be able to move and would probably be the least efficient because of the law of degradation of energy which would leave you with 10% usable energy degraded from 100% solar energy. so to start at the closest point of where it could be deduced it must be electric, but is there any way to eliminate electrical resistance? then it raises the question of the existence of a material which is a perfect conductor, doesnt resist electron flow, wont create heat. that is the efficiency of amperage, if a circuit could be built with such large wires to carry large voltage and negligible to no amperage. but then even if you could build this incredibly heavy low amperage circuit and use it to power something, what the hell could you do with it?