So the stupid thing broke and has been rattling around on the exhaust pipe under the car. Is this piece necessary or can I just remove it?

 

I'm assuming your talking about the catalytic converters heat shield since the manifolds heat sheild doesn't go all the way around the manifold. If your not noticing any performance problems then I don't see why you can't remove it. I mean it has broke off already so just take your saws-all and cut that thing off.

If it is missing a piece from the cat you will need to buy another one to pass emissions if they are strict in your area.