Expansion chamber design is a rabbit hole. Since I've started playing around with bikes, I've seen expert information that conflicts with other expert information. The physics involved are a hot mess. Some pipes 'break the rules' but produce fast results. The point is that any pipe design is a work in progress, and you should expect some trial and error if you want fast results.
-Moped Army forums aren't really the best place for this conversation, as there is a TON of misinformation around. If you want to learn more, I can recommend a good read: