mr h

i own a 2007 honda civic LX Sedan, with a 1.8 L i-Vtec engine. I want the car to give off a deep performance sound but i do not want to do any major mods like cold air intakes or turbo kits....i want to know if i add a performance muffler without any engine mods will it slow down the performance of my car. or is the 1.8 i-vtec STOCK engine powerful enough to still give off performance with a large muffler. ( the car is an Automatic ) Do Not Want To Change Transmission To Manual.