This might sound stupid but what exactly does a catalytic converter do besides restrict airflow. i thought they used to filter out lead from gasoline but we use unleaded fuel. i could be wrong though on what they do.

 

I has a catalist in it. I think its platnum. Anyway when unburned fuel goes through it, the fuel is burned so that the car has less emmisions. That is why they get so hot. basicly it finishes the combustion cycle. It also makes the car a little more quiet.