Restrictive Mufflers

I'm going to redo my exhaust system this winter and I'm taking my old stuff apart. I have Accurate pipes and mufflers on it now and want to replace the 2 1/4 pipe with 2 1/2 and new mufflers. Out of curiosity I cut an old muffler apart and I was shock to see how restrictive it is inside. Although it ran well and sounded good.