Quiet mufflers

imco SL 422. i think is the right part number.they are basically identical to an imco/summit turbo muffler just with a longer case (18").i have them on my 4x4 truck. dual 2.25,and they are very quiet.as far as the best flowing quiet muffler.....id look to see if they make a dynomax ultra flo with a large case.i just replaced the thrush welded on my dart with ultraflos and it is night and day as far as noise goes.