Yes you will get a code for the downstream O2 sensor. You can try using a J-style fitting with the smallest restriction insert (store.specr53.com/products/vibrant-performance-j-style-o2-sensor-restrictor-fitting.html). My car is still street legal so I have to get it smogged. I had a cat fabricated from this Flowmaster unit (store.specr53.com/products/flowmaster-universal-catalytic-converter.html)
Update: After a single track day, the flex joint broke. The length of the collectors means there isn’t much room for a large enough flex joint. Time to test another design.
