full exhaust vs. cat back

they are the same. you have a header (or turbo manifold) then a Cat. then the exhaust.

no it dosent replace the cat. it goes from the flange directly behind the cat. all the way back.
header, flange, cat., flange, (this is where your cat. back goes)

edit: on NA cars bigger is not allways better, i have a ga16de, if i get over a 2in. diameter pipe i will lose alot of power in the low end. you need to figure out the correct size for the 300z. all cat backs are not better than stock, pace setter makes a cat back for my car at a 2.25in. diameter and i would lose alot of power in the low end so my car would be a super slug untill it hit maybe 4k rpm, and since i have an auto it would be even worse.

nissan cats are very good so you will only gain maybe 1-2 HP tops. the best thing to do is buy a new exhaust, go to your muffler shop and have them make you a 2inch exhaust with the muffler of your choice (magnaflo is very good and sounds great, not tinny) then buy a glass pack muffler to use as a resonator, use the biggest possible so it will mello out the sound. and leave the cat on, or you could buy an sr20de engine cat to use. also, you cant take the cat of the GA off unless you take your manifold off (its attached :thumbup: )

but a turbo with no muff is much more quiet than an NA with no muff. (nickzac said it best> will sound like a tin can full of angry bee's