Just got thru installing my new system used a dynomax 3" cat back pipe into a 2.5" flotec avenger duel outlet muffler with dynonax 2.5" tailpipes only complaint is U will need an extention on the drivers side to hit the factory mount. here in Ct. it's now emissions exempt co the cat is also a memory the sound is sweet not loud enough to tic off the neighbors but really barks when smacked have gotten a lot of compliments on it from other f body oweners
Biged

 

so u went from a 3" i-pipe into a 2.5" inlet muffler?

 

I think he means a 3" inlet (in to the muffler) and 2 2.5" outlets.