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.
You need to separate boosted and naturally aspirated. Boosted will still function just fine with a stock throttle body. You need to start looking at larger throttle bodies when you start moving larger volumes of air. The throttle bodies that dap and moe's sell are ported with stock butterflies, so all you are doing is creating a smoother transition of the air to increase velocity, not flowing more volume. I would look at going to an 87mm with headers and full bolt ons because you want to flow as much air at higher velocity to clear the combustion chamber as quickly as possible.
Anything beyond bolt ons on a naturally aspirated motor should have a larger true bore throttle body, and any good engine builder will tell you that.