I'm no mechanical engineer, but I do know that ALL bi-metal springs contract with cold and expand with heat. As a matter of fact, everything in the universe contracts with cold and expands with heat. That's just physics.
I believe the differences between the two types of springs (Rochester -vs- Holley) is the way their made (?)
Bi-metal coils consist of two strips of different metals, which expand (or contract) at different rates as they are heated (or cooled), welded together back to back. (That part I'm positive on!)
(Here's the part I'm not so sure of) The metal that expands faster is on one side of the strip for one type of coil and on the other side of the strip for the other type of coil (?) This would make one coil move down when heated and the other move up when heated and vice versa, but again, I'm not sure if this is actually correct.
I'll see if John or any of the other guys can add anything to this.