Seldom,
Down load the link to "The Two Stroke Tuners Handbook" by Gordon Jennings. Great reading that is easy to understand and his expansion chamber calculations work. I used them for several dirt bike expansion chambers I built in the 70s. He is also the originator of my favorite one liner: "Dilute my ignorance"! Great book, great guy, he wrote for Cycle magazine, and he passed away a couple of years ago.
Rex