Friend of mine went from a dual 2" (86 camaro) to a single 3.5" with a 3" Y-pipe and picked up 6/10th's. No joke.

I think you won't see an ET difference with 3" to the mufflers & 3" tailpipes to 2.5" tailpipes, due to the mufflers.

When it takes more than a sweet mullet to prove you rule at the trailer park..