I worked at a tool and die shop where improper heat treatment cost us over 300K. Spring steel isn't something you mess with the temper on... this is not "what I read on the forums" this is facts about how heat messes with the properties of steel. The problem isn't in the coils you actually compress, those are effectively made irrelivant (so long as you don't ruin the temper so much as to cause them to physically break).. the problem is in the area which is effected by the transfered heat.. you end up with a lot softer steel than you had to start with because it is not being quenched.. Its just not something that is wise to do unless you know EXACTLY what you are doing, and in order to do it properly, you probably need a mechanical engineering degree, with some specialty skills in tempering etc..