Whoa dude....you need to get a 3" downpipe before the headers. The stock downpipe has a ubend behind the cat that restricts exhaust flow. If you get headers, some of them come with a downpipe with a cat. But if you dont go headers just yet, make sure you do something about the downpipe. I run a 3.4 with the mods I have with very little knock. I had about 1-2 degree's and the mini afc 2.0 took care of that.