In reality, it depends on what cat you have and what condition it is on. If you have an old and clogged cat, it will make a HUGE difference. If you have a fairly new high flow cat, it will make little difference (although still SOME difference). IS it worth it? Not really, as, if you run your Jeep in the US, it is illegal to run without a cat. Same here in CR, but I am considering loosing mine because it IS legal in Panama to run without a cat.