what are the benifits of having a y-pipe?
im putting headers on my car and wanted to do a custom true dual exhaust, headers then exhaust cutouts then 2.5" pipe to two glass packs. the headers i bought came with a y pipe, but would it be a problem not to use it?

 

If you're doing dual exhaust you don't use a Y pipe, a Y pipe is meant to merge 2 pipes into 1. If you do duals you would usually install an H or an X pipe to equalize pressure in the 2 banks of exhaust. I will tell you this, I put duals on my car and if I had the parts on hand to just run a 3in single exhaust I probably would've been happier with that. Running the duals for me lost me some ground clearance.

 

do i have to run a h or x pipe?

 

h or an x pipe is an option. it just evens out the flow between the two pipes.