1. How do you measure the size of the collector? Do you use the inner diameter or the outer diameter?

2. Is there a way to tell the difference between a JDM DC header and a USDM DC header?

If anyone can answer either or both it would be greatly appreciated. Thanks.

 

I believe it's the inner, but I could be wrong.

The JDM DC is 2.5", the USDM is 2.25". I'd check both diameters and see what they come up to. You should know by the time you're done.

 

Thanks,

ID is only 2", the OD is 2.25". I guess I've got a USDM DC Header than.