A good high flow cat converter willl do the same job as a regular one. I have one on my car and my car passed with flying colors. In fact, I ended up getting the abbreviated testing on my car because the emissions were low. But, not all c/c's are made the same and you get what you pay for. So, at the very least make sure it's one that's legal in 50 states (american standards). Mine is made by magnaflow and I paid 95 at Lordco. Or check with Burnaby Auto parts. A well maintained engine that is in good running order (to factory spec) will always pass, even if you put on some performance enhancements. But the more radical the performance enhancement, the more the engine goes off factory spec and the likelier that it will fail aircare. If your C/C needs to be replaced, then it might solve your NOX problem too.