I have a Calif. emmissions 2004.5 lly and I want to uprade my exhaust system. If I go to a 4 inch exhaust with muffler and remove the cat will this alteration make it cop a code? Is this the way to go or do any of you guys have any better ideas? I presently do not use a performance device I just want to lower my exhaust temps when I am towing my 5th wheel. Any sugestions will be:) :) greatly appriciated.

If you pull the cat, you may or may not get the Check engine light. If you go with a cat-back system, you will not throw any codes. I would leave the cat in place and go with a cat-back system like the MBRP.

If you leave the cat in place you will not get nearly as much of an egt reduction as you would if you removed it. If you remove the cat just add a finger stick to stop the code. Also, if you remove the cat hold onto it, you may need it to pass a smog if they start testing in 2007.

Removing the cat does not produce much more HP, according to Banks when I had mine put on, besides getting caught with it off will cost $$$$$$