A simple 3 stage two stroke exhaust calculator based on formulas of G.P. Blair from the book: The Design & Simulation of Two Strokes.
You can also save and load the data by using the provided functions.

Note:
This coefficient Kh is called the horn coefficient, with typical values between one and two. Small values of Kh are best suited to Grand Prix engines with narrow power bands, larger values are for wider more flexible engines.