ok right now on my 91 explorer with a 4.0ohv, i have a k/n cone filter, 66mm bbk tb, hollowed cats, 2.5" flowmaster exhaust... i love the throttle body, and i like my exhaust it could be louder and deeper but its a v6.

first i want to start with the intake, i goin to put a the stock intake box back on and a k/n air filter inside it, and drill a 3" hole in the back of the box and put this 3" pipe/snorkle.

what intake pipe size should i get bent up? 3", 3 1/4", or 3 1/2"?
im gettin a stainless steel one for looks anyways soo i want to maybe get some performance

and then....
i want to get rid of my 2 hollowed cats for 1 magnaflow unversial high flow cat 2.5" in/out and have custom 2.5" pipe put on after the y pipe and before the exhaust.
i heard having hollowed cats kill you mpg and backpressure

also, i think im gonna spend the cash for heddman headers, soo then i have a complete exhaust setup, and that should be good for atleast 10hp over stock

oh and also i want to get a gibson slash tip 2.5" in/3" or 3.5" out and 8" long, now would a tip like this make my truck louder?