2001 4.6L with straight 2 1/2" pipe turned-down, and Flowmaster "Y-Pipe". I want it to be louder as well as hopefully see a slight performance gain. My idea was to have the stock pre-cats cut out or gutted while retaining the stock main cats. No need in replacing them if they're good, especially with the crazy O2 setup. I do not think I will have a CEL issue with this setup either. My question is has anyone done it? I want to know what difference it made to sound / acceleration, and tips on getting it done. I cancelled my factory warranty so I don't care about that, and I have about 45K mi. Thanks!!!

 

i have no cats on mine and for the elbow cats my uncle cut some pipe at angles so it would curve down to where it needs to be.works pretty good.