I am doing an engine swap now. I am getting rid of the AIR pump and going with headers. Should I go with 3" from the collectors to the cat and 3" from the cat to the muffler and 2&1/2" duel out? I have the Magnaflow 12267 muffler and will go with a 3" in and out Magnaflow cat. Or I don't have smog so I don't need the cat. But I just don't want it loud. I want a low rumble. Should I go with the cat or will it be to loud with out one. Is that the rite muffler? It is small. If You have any input and preferences please let me know. I have a 3" Magnaflow cat back on my 98 T/A and it sounds great that's why I went with them.
This is a one time deal and I just want to get it rite.

 

I have 3" collector. cat deleted to a hooker muffler with dual 2.5 outlets. Nice rumble but not too loud unless you get on it.