metal spring technology

[Jbird]

hello all, can any one advise me please on how to calculate the following; I want a torsion spring that has closed to open length of 350mm and i expect that the force that will be exerted to open it will be about 150lbs, what i am after is what is the relation ship between energy used and energy returned , also how does one go about looking for a hard spring or a soft spring and there for how would this effect the length of the spring ? a rudermentry or rule of thum answer if possible