ClubCJ - The CJ Lancer Club

All good Robin hood
If you decide to get the cat swap done might be wise to shove a mini-cat on the rear sensor, the ECU will eventually crack a sad.
Fireup Google and search on
O2 sensor mini-cat
Make sure to get the one with the honeycomb inside , don't get the hollow core.
https://www.carmodsaustralia.com.au/cel ... h-mini-cat
These ones work, however , far from the greatest price around you can get them for half that , these are the style of unit to get
Don't buy it from the exhaust shop , they usually sell them for $100 so they can fund their Christmas party with, they are usually sitting on their front counter next to the idrive units

If you swap out the cat for a 200-cell, would a mini-cat on the sensor still be necessary?

Yup

You will need one of the mini cat to out over the rear O2 sensor

The O2 sensor , think of it as your nose.
It lets you smell a variety of smell.
The rear O2 sensor is used to smell the exhaust after it goes thru the cat.
It does this and the measurements are converted to a voltage.from memory it is from zero to five volts.
This voltage is then used by the ECU to check and see if the cat is actually doing its job.
Seeing though you haven't edited anything in the ECU it still think you have the OEM cat.
So after while it will eventually crack a sad and give you a CEL.
However, if you shove the mini-cat over the rear O2 sensor this is more then enough to keep the voltage in a safe zone as the mini-cat uses the same substrate as the main cat core does.

Ahh, good stuff. Cheers.