I've never heard of many people having much luck with changing to a high flow cat on an obd2 car. reason being it doesn't drop enough emissions through the cat to not set a code with the after cat o2 sensor. Personally I think it's a waste of money to waste time trying to gain horsepower from the cats, honda's cats are usually pretty free flowing as it is. I removed mine and put a straight pipe and if anything it just feels like it lost low end power.

 

i have a carsound cat and the muffler guy had to make a "makeshift" hole to place my o2 sensor...maybe it was poorly done...however, i did drive with a bad, bad o2 sensor for a few weeks before i replaced it...could that have messed up my cat?