i just found out that i have 2" exhaust with the stock d15 cat in it. But i have a b16a2

So im about to replace the cat. should i find a real b16 cat. how restrictive is this.

 

I would think it would be the same D16 to B16. They are the same size motors.1.6l

 

True, but the B also flows more CFM through its head then the D, so I doubt the cat for the D is optimum for the flow of a B. CHeck out the EG Civic project car on http://www.sportcompactcarweb.com. They swap the B16 in without changing the exhaust, and they did see a loss of power compared to a proper sized system and cat.

 

I don't know about the d15 cat, but for the 99-00 EX and Si the cats are the same.