I'm not sure about Dynomax, but it is easy to figure out what muffler is restrictive. Just look inside of it. If you can look through it then it is not restrictive , but if you can not see through it, the the exhaust flow will habe to go around or tough what you see in there. If it looks like a pipe with small holes on it, that's not restrictive. Also if these holes have little ears on them , then these ears need to go in the direction of the flow. You don't want them to catch the flow as it goes by. This would be a restriction. Also the longer the muffler is , the quieter it will be.