Well I am in the process of building my veg cab, and I am a bit confused regarding the PI size. If I have a 4 inch 160 cfm CPU fan as an exhaust, then theroretically, my PI should be 8 inches? That just doesn't seem correct. Should I just have 2 - 4 inch PI's? Shit, maybe I even have it backwards, but I thought the PI should be twice the size of my exhaust.... Thanks in advance!