There is something more to it.
I don't mean to be rude at all but I think that you are quite far away from being able to understand this. I can recall studying some parts of this in University Physics but I have forgotten it all now so I cannot explain it to you.
A Google search for [thermodynamics engine efficiency] turns up some good looking links including:-
Thermal efficiency - Wikipedia, the free encyclopedia
"Surprisingly, even an ideal, frictionless engine can't convert anywhere near 100% of its input heat into work."
I think that you will find that there are NO shortcuts.
First year university maths and afterwards a thermodynamics course is what it will take.
If your reaction is No No No No - why is it not possible for an ordinary person to figure this out - then have a go at designing an atomic bomb, or a jet engine.
Of course a perfectly ordinary person CAN do these things given a decade of study.
Good luck.