https://www.c-f-m.com/performancepa...s/pc/FSWerks-4-1-Race-Performance-Header-for-03-16-Ford-Focus-Duratec-p1313.htm

the fswerks has 1 7/8 inch primaries and a 2.5in OD collector.

 

How much do you have to lengthen the header for the mk3 focus? Is it worth upgrading from the eBay header?

 

I'd just stick with the ebay header. The fswerks is about 1 inch short so you dont have to lengthen it to much but it sits really close to the front sway bar so under hard acceleration you get some tapping there.

 

For thing is to get a poly dogbone to take advantage of a header.......