Is catco 2 way or 3 way? also some ?

[Ninetyfive240sxSE]

also are most hi flow cat 2 way or 3 way? are the cat sold on muffler shop to replace stock cat a 2 way or 3 way?and is it worth to get an oem cat if ur running an srdet20 to pass emission? i heard everyone agree to retard the timing -1 degreebut for the lean/rich mixtures not sure yet... some say to run the engine lean and other say to run it rich as it helps nox to go down, but will bring hc up.

any input helps

[180fan]

2 way, no NOx scrubbers in there.

Go with the oem cat, if you're in a jam, get two and have them welded inline. Get the stock downpipe as well, keep the carbon canister, retard timing, and also get the stock airbox, all those things are necessary to pass your car in CA and even then your NOx count will be high if you can get someone to pass you out the pipe.