Well, if you enlarge your exhaust.... you lose low end HP and gain SOME upper HP. My opinion is keep the stock sizing and just open up the exhaust (y-pipe) SVT style or better. Either use chambered flowmasters at the tail pipe with a straight through resinator in the center or vise versa.
As far as intake goes, smooth airflow gives the best gains via SVT's extrude honed UIM. In that aspect, you can replace the accordian tube with an aluminum pipe style setup. The ultimate setup would be an intake pipe that expands from TB size to 3" where the 3" end of the accordian tube used to be. Then the sky is the limit. Keeping stock lengths and sizes is crucial for overall performance. Or if you just want to take the easy route and spend more money losing in the lowers and gaining in the uppers then go for it! It seems kinda pointless to add a bigger exhaust system, unless you plan on flooring it everywhere you go. If so, be sure to put back alot more money for gas, oil, maintanance, and speeding tickets!
