"Why are you not going with what you used to do to hit the big numbers?"
I am. The manifold isn't made for mopeds. I modded it. That is another thing we used to do. We didn't always use a cut off header. We used it so we could point the pipe up because it looked cool! It would exit just below the seat. Looked cool as hell. I bought a pretty big exhaust with side bleed and it would not look good upswept. I did have to buy a modern pipe because good luck finding a Proto Pipe which was to the best of my knowledge the first chamber made specifically for mopeds. I would love to find one but as I said good luck with that. They came out around 1979 or so. (edited)