what is this part?

ijust took my exahust off to drop the trans. and well right after the cats on the stock "h pipe" (mid section) there is a tube that is connected to the exhaust. it then leades up in the the enigne bay to the motor. what is this piece for?

That is called a Thermactor Tube. Which goes to your smog pump.

That is called a Thermactor Tube. Which goes to your smog pump.
Which also runs to the back of the heads.

is that needed? can i just plug it?

I would re-install it unless your going to plug it all correctly(pain in the ass). Also most states you will fail inspection if it is not there.

That's true. But they don't do Inspection's in Michigan.

how do you plug it correctly