I just got a new Summit catalog and note on their page 68 they show "Supertrapp Replacement Components" as Muffler cores such as SUP-400-1140 but they don't give the diameter or length so you would need to call the folks at Trapp. I note with considerable amusement that on the same page they show "SuperTrapp Muffler Endcaps" such as SUP-402-3046 which look a LOT like what I used when I cut the bottoms off of aluminum beer cans!

Don Shillady
Retired Scientist/teen rodder