Downpipe sizing advice

[bNasty]

Ok so i did a search and found nothing and sorry ahead of time for the newb question but on the punishment racing 3 inch dp it says it has a 2.5 inch entrance now is that 2.5 to the o2 housing or 2.5 to the rest of the cat back... its going to be mated up to a greddy ti-c exhaust fyi

 

[1gDSM4g63]

It means the entrance is the standard Mitsubishi o2 flange while the rest of piping is 3". So unless you're using a v-band turbo or a custom fabricated o2 housing you'll need a standard Mitsubishi o2 flange entrance.