Tony, there are numerous books and sites on the web that have formulas for building pipes. Why bother though. you could simply buy a tuned pipe for a simular sized kids motorcycle and mod it to your specific requirments. I bet a Lem or Cobra 50cc bike pipe would work great on a saw with a little work. KD actually runs Yamaha kt 100 kart pipes on his piped 3120's and I believe 088's also.specifics are a little harder to get here.. good luck.