I remember reading about the Cobalt SS S/C specs and I noticed it said something about sodium filled valves. What's the significance of this kind of engineering? How does it make the engine "better"? All I know about sodium is that it is one of the most reactive elements, that I know from college chemistry haha.

 

When the engine gets up to operating temp. the sodium turns to liquid and greatly helps valve cooling, and resistance against warp.

 

Like Blown said, and because of that I believe it helps increase long-term reliability.