What I would like to do is remove the stock y pipe, and instead run custom pipes out of the stock manifolds and dump them into a dual in/dual out flowmaster HD muffler. I think this could yield some extra horsepower, and some extra flow oppose to the bottle neck I presume is occurring now. Here's a scrappy pic of what I mean.

 

Reason I am trying to consider this option is because I like the flow a "true dual" provides, but hate the extra cost for double the mufflers, add in a x pipe, and still maybe get a weird funky noise out the rear. I like this concept because the muffler acts as the cross over pipe, yet the mufflers internal chambers are so large that I think it would easily provide the same flow as a real "true dual", without the hassle and inconsistency they often present.

 

Just realize that your engine wants some back pressure and too much flow actually reduces horsepower in some rpm ranges if all other things are the same.

 

Yeah I considered that possibility. However, I think the 50 Series HD will provide plenty of back pressure on the system, am I wrong? No worse than my straight through magnaflow right now.