Get an off-road H-pipe, then your cat problems will be solved. But if that is not what you want, then I will try and help you. It will be running really rough, and your exhaust coming out of your tail pipe/turn down, whatever you have, will not have much pressure to it.
I have an x-pipe on now I do hear an occasional rattle will the car pass emissions without the cats? I remember when I got my flowmasters they change one of the cats to a low restriction cat but if I don't need them iI don't want them.
not so sure about the emissions thing. Oh, and my father said that one way to check it is when the motor has been running for a while, look and see if the cat is glowing red, because if it is, that means that all the exhaust is getting backed up there.
if they put any type of probe in the exhaust stream for your emissions test then you will most definately need the cats. another way to check them would be when it is cold, tap on them with a rubber mallet, and if they rattle, then they are in pieces.
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