How much better, if any, are JDM headers as opposed to regular ceramic? And will either of these fit a 3" exhaust planned for the future? sorry for being a noob, plz help ops:

 

"JDM headers as opposed to regular ceramic"???? I'm assuming you left out "SS" or something. Anyways, the OEM ITR JDM 4-1 is not ceramic coated and is steel (not sure what type tho, sorry). DC Sports makes both SS and ceramic coated JDM headers. They have 2.5" collectors so they will not bolt right up to a 3" exhaust. But dear god, why do you need a 3" exhaust anyways? You can make a LOT of power with the stock exhaust and if you want more there are a number of very good options that are 2.5".

I'd only go 3" with boost and in that case a topic on headers it completely pointless.

 

Dave said exactly what I was thinking. Sounds like you are confusing collector size and material as differentiating factors of USDM and JDM headers.

3" exhaust is way too big unless you use turbo and then a header is useless.