neither do I.3" exhaust will definitely help a BBC breath over 2.5". I'm running a 10:1 compression 383 stroked SBC with 3" tubes from the headers back. At first I was running 40 series Flowmasters and they were just a tad loud for my taste. I switched to 50 series Flowmasters and it is just right. I have to say mufflers are a personal preference. I personally don't like the sound of Magnaflow mufflers.