It was a 14.5-1 406; the only reason I ran em that big was $$ I paid $40. for the headers; I ran the 2 1/2" a couple days before switching to the big headers and still didn't notice any change(no dyno or drag tests)that's a large primary for such a small exit diameter.. what kind of motor were you running it on?
I think the average glasspack muffler is not much better than what the factory installed--just loud.I always thought glasspacks were suppossed to be a high flow muffler,