Stock 318 exhaust reccomendations

The Summit e haist system is nice. True duals. There mufflers are quite t idle and mello at cruise. For a more aggressive sound, choose the Dyno Max Turbo muffler.
Exhaust piping IMO for this particular set up would be 2-1/4.

You'll add a modest amount of power and some mileage.
(Add a MSD for some extra mileage. A basic 6A box will do just fine.)