Thinking of exhaust mod

An exhaust system is a function of flow capability based on the engines needs. Basically, up to 500hp, 2.5" is all thats needed. The critical point is the amount the mufflers flow in CFM. Usually, people put more than enough pipe, then put mufflers on that don't flow as well as the pipes. Generally speaking, straight through style mufflers are the only ones that flow as much as a straight pipe. Dynomax Ultra Flow and Hooker Max Flow are good examples. For your 318, I doubt putting any type of crossover is necessary. Besides, I would venture to guess that any local muffler shop would ruin your exhaust doing so. I have had so many BAD jobs done at exhaust shops, I have a bad taste in my mouth for any of the compression bent systems that get done.