Short answer: Yes. 2.5 inch coming out of the cat, going back to the Y split then into 2.25 inch quasi duals is what I have. Some have true duals.Some guys have maybe 3" catback to the rear y split, but I don't figure you need that with a 2.5 NA engine. Better flow mufflers may be worth say 1 hp or so by themselves. All kinds of research was done on this topic 10 years ago or more. I hated the stock y pipe, even optimized and msds y pipe is not much better. I'd rec you look at the simple design of the BAT y pipe, same as what SHO Shop used to do, using a 2 into 1 cat. I feel that y pipe set up was worth like 4 hp by itself, more when used with other mods, optimized stock was maybe worth .5 or 1 hp by itself. There are standard 2 into 1 cats out there, maybe matched up with some simple pipes from the manifolds you can do the same thing for a competitive (cheap?) price. The original Mr. CEG, founder Lance, had the Sho Shop Y as did I.