Quiet muffler for 2 1/4 exhaust

A quiet, non-restrictive muffler really doesn't exist. First, quiet is very subjective. Some consider no mufflers too quiet, other consider an electric car too loud. You will trade off noise for flow when looking at bd/flow ratings. With that most in the performance crowd either use the large case Dynomax Turbo muffler. For a bit more sound the small case Dynomax Turbo muffler,, then a generic Turbo, then a Magnaflow type muffler, after than it just gets louder. A single 2.25 " system with that quiet flow will probably be decently quiet. Add a resonator and things will be pretty quiet.