Does anyone have experience making their own high flow catalytic converters for our x308 models? I was thinking of making my own since the only ones I know that still make this upgrade is paramount performance for +$1600. I have access to a machine shop, so not having the right tools is probably not an issue in my case.

Is this feasible? What is the best approach to this? Any advice? Are the O2 sensors going to be a big hurdle?

I did on my Vette 25 yrs ago, ....a piece of rebar and a 4 lb maul and 15 minutes later I had high flow.
Actually I believe there's a couple youtube vids on making your own.

I'd suggest taking measurements of how far the sensors go into the cat, they're sensitive to temps. I had to fit adapters to my high flow cats to get them running right.

Where'd you get your high flow cats from? By adapters, do you mean an extrusion from the cat, where you put the threading for the O2 sensors?

All you need is a couple metallic substrate high flow cats/piping/welder and fab away or any exhaust shop can do it. If you get cat efficiency codes you will just need to add rear O2 bung spacers. My '98 won't throw a code even with no catalytics installed, but i've heard of people needing to add rear spacers on later X308 years with hi-flo's/cat delete

I have a 99 so maybe mine won't throw a code either... hopefully. Do you happen to know if the diameter I need is 2.5 inches? Also, would a 100 cell CAT be better than 200 cell?