BOV Flange HKS SSQV
 

http://www.dynamicturbo.com/products...ff-valves.html

Being a retard here, what is the difference between flange sizes?

I have 2.5" IC piping, which is 63.5mm I know, but which one do I need?

Apologies in advance.

Really? Nada? Shoulda put this in "general", actually get hits there :-D

It's possible they changed the design of the flange with the different revisions of the valve. Usually when you buy something like this it just comes with a flat flange or something. This is just a guess, though. Maybe call them?

Get the one that is closest to your pipe diameter. You may have to grind on it a bit to get perfect fit up before welding. My only suggestion is if you are getting a cast aluminum flange to make sure that it is high quality and not like the pot metal junk I have. It's very hard to weld.