I forgot to put that metal plate on the bottom of my intake when installing it. Do I need that? what does it do? it has 3 little holes on 1 end??

 

That's a heat shield used to keep heat in the lifter valley, not in the intake manifold. You'll probably see higher air intake temperatures inside the manifold. It's not crucial, but recommended that you have it installed.

 

This should hinder your performance. Probably not noticable by any means but probably measureable on a dyno. For what its worth.

 

O, it will be noticeable, but you can get by without it. First time you sit in traffic you'll notice it.