I'm putting new exhaust on my 89, and thinking of getting an off-road x-pipe and having modern 3 way non-smog cats welded into them. All of the available catted midpipes have smog cats, but my rebuilt smog pump already sounds like after a couple months and I would like to remove the system but still have cats. But, as I understand the modern cats can run without smog because modern engine computers run cleaner and have downstream O2 sensors. I'm wondering how well modern cats will work with just the stock ECU and O2 setup.