CARB SPACERS

Generally, the idea goes like this:

4 hole is better for low end because it makes hte airflow more directional

Open is better for top end because it flows like crazy.

I have a 1" aluminum open spacer on mine, because I just can't fathom putting a 4 hole on, since in my mind, it just looks like a restrictor plate. A phenolic spacer will help even more with heat isolation.