Here's my thoughts: If you are going for big power, or +300 HP, then change it out. The stocker is decent as long as it's not beat to hell (take it out and dump a bunch of gas in it to clean out all the blow by built up in it throughout the years if you wanna keep it). My cousin has a full 3" exhaust (with the same DP as I've got, actually, exact same setup as mine) along with the full hardpipe kit on that link I posted too. The stock IC is still there and he has a SS air filter also, everything else is stock. We installed all of it at the same time and it was a night and day difference in throttle response, spool up, and overal power .