Just a fyi not running cats and no tune with have zero affect on performance. The rears do not control any fuel trim tables or anything of that sort. So no it will not harm anything. It will set a cel or mil but it will not limit power or anything of that sort.
What they do is position the REAR oem O2 sensors out of the direct path of the exhaust. Then no more P0420 and P0430 codes being thrown. If instead, you just delete the rear O2 sensors in a tune, then u will get busted if tested for emissions. These days, instead of inserting an emissions probe into the exhaust tips, the various agencies are now plugging test gear directly into the OBD port.
In extremely rare cases, 2 x O2 extenders have to be stacked...but I only know of just one case.
My 2010 started throwing the P0420 and P0430 codes right after the JBA LT's and mating JBA hi-flow cats were installed.
The resistor-capacitor network for a catless system will also work, as posted above.... provided the agency involved doesn't look under your car....and see missing cats...hi-flow or oem.
