Questions the title.

Reason for the question is because, I sold a catback exhaust off a Type S to a friend of mine who has a base automatic RSX. He said the piping didn't fit the cat and was about 2-4 inches short. I'm not sure if he installed it wrong or not and I haven't seen it myself so I don't know what he did wrong, if he did. Please help. TIA!

 

That sounds exactly like trying to fit a EP Type-R exhaust onto a USDM Si -- the catback piping is definitely shorter.

He'll either have to have an adapter fabricated to make up the missing length or get header/cat parts made for a Type-S (OEM header & cat, or race header, or whatever).

I posted a thread last fall about fitting a CTR-spec Fujitsubo catback onto my EP by using stock RSX-S header & catalytic convertor. It wouldn't surprise me at all to find that the base RSX uses the same header & cat as the EP3 Si.
https://honda-tech.com/zerothread?id=1365602

 

Yes, a catback exhaust for a base RSX is different than a catback for a Type-S.

Every manu. has a diff. part number for both.