I had a custom 3'' true dual system built for mine but I am doing a motor swap and probably forced induction so I figured I would need the extra diameter. better flow is always the key to building power in anything. I believe when its all said and done I will have roughly 400 cubes and hopefully about 12-15 PSIand so on and so on....the usual list.

- to answer your question, a naturally aspirated 5.3 would never require 3 inch... I was just proactive on getting mine fabbed up for the eventual swap.

- mufflers... this may sound funny and some of you may never had heard about this before but I actually had some 24'' glass-packs turned backwards. when they flow reverse they become resonators. it sounds really mellow but with good volume. when you get on it, the sound is great but without the usual popping of a glasspack. ask Z06 DREAMING he can tell you what my system sounds like. I'm happy with what I have and it wasnt that expensive. I have it dumped before the axle with some nice little chrome tips you can see through the wheel well... ooooohhhhh sparkly.....

 

If you're gonna stay basically stock with bolt-ons, 2.25" will be fine, but if you plan on doing a cam or going FI, you will definitely benefit from going a little bigger.