I'm going to run my headers, cats, and dual pipes to a dual-in dual-out single muffler. Any need/benefits of installing a H or Y pipe?

 

If you don't have alot of horsepower, it is more beneficial to run a cross pipe. If you have alot of horsepower, you would be better off running true duals. But in all honesty, it won't make THAT big of a difference...

 

If you ran true duals, a crossover would quiet it down a little and avoid some resonance. But if you're going to a dual in - single out muffler, it won't make any difference.