will this header fit my exhust? if not then how can i make it fit?

 

why would it not? the header connects to the cat which connects to the exhaust...so you're question should be does this work with my cat. unless it's a long race header that links to the exhaust...which would still be a yes.

 

let me make it more clear
my mods are 4-2-1 header with apexi n1
the apexi is 2.36 in diamater
and im planning to replace my old header with a kami header (2.5in) would this be a good choice for my jrsc or should i stick with my old header? do i have to replace the cat so there wouldn't a choke