just wondering are there cats that go from 2" inlet to 3" out? or test pipes if so where could i find one?
Why? Just get a 3" high flow. Its fine going from a smaller diameter to larger.
so a 3" cat will bolt up to the stock downpipe on my ka24de?
I haven’t seen anything like that, there may well be something, have you thought of just welding a 2" to 3" reducer on one side of a normal 3" in/outlet cat?
Yessir
3 inch may be a touch to big for NA i would go 2.5 at the most
my 2 cents.
3" is fine…car is going to be boosted within the next month or so ive got a good deal on an apexi exhaust so…
if u are going to be boosting it then dont put the exhaust on yet. Wait until u have the new manifold and downpipe on. then u can just get a 3 inch downpipe. problem solved.
x2, plus it’s much easier to do it off the car, then having to srtuggle with it while its still all mounted and such.
Its not that hard to put on an exhaust and cat under the car… 
why do a job twice when you can just do it once when u boost the car?