Originally Posted by ironchef2011
According to Moe's, it's an 85mm for all bolt ons including headers. Forced induction is for the 87mm and higher.
This is somewhat correct BUT if running headers you'll want 87mm
Let me tell you why.
The extra airflow from the 87mm will help if you can get that air out just as easily which is where the headers come into the equation.
But even without headers you'll notice the difference from 85mm to 87mm