Well, would putting the cat behind the flex be a problem?
I'm assuming if people use race headers to delete the cat that our flex pipe is ok without a cat in front of it.
So we need to find out how the ZX3 catback works, when fitting it to a sedan do you add the extension before the muffler, or after? I'll try and find out. Hopefuly it's before the muffler.
If it is before the muffler we can move our cat behind the flex pipe. I'm not exactly how long out cat is, but I'm guessing with flanges on both sides it will be just under a foot? so maybe the ZX3 cat back will fit perfectly, but maybe even the ZX3 cat back will be too long, so any cat back system will have to get chopped shorter, and most places the zx3 is cheaper than the sedan.
new questions are now-
Can the cat go behind the flex? (legally and safely without causing any harm)
How long is our cat-converter?
Where does the ZX3 cat-back system need to be extended to fit a sedan?
I still have a Focus parked, I might fix it up one day.