Professor Blair's tests proved that the return waves timing can be calculated fairly closely using the straight distances and the pressure wave speed in the pipe for that distance. He also proved that the return waves are generated all along the length of the diffuser and baffle cones. So I put formulas based on that in an Excel workbook file to analyze an existing expansion chamber, or help design a new one, based on the timing of the return waves in relation to the timing of the ports. In 2016 I discovered Blairs research paper about his dyno and a karting engine where he gave full details, including exhaust gas temperatures and pipe return pressure waves graphs. I then fine tuned my formulas to match his results for the pressure waves and horsepower graph. It also agrees with different customers horsepower graphs. The spreadsheet includes my equations for:
1) calculating for the temperature loss in the exhaust gas all along the pipe based on the outer diameter which serves as a conduit for the heat to escape through the metal.
2) simulating return waves strength and form based on the psi changes every 10mm (which creates the return wave) from expansion or contraction of the cone diameter.
3) calculating how to use the return waves graph in relation to port open timing to derive an estimated pipe power and powerband.
4) calculating the exhaust pulse time duration based on RPM, engine size, and exhaust port dimensions. This is important because it determines the time duration of the primary return waves.

Out With the Old:
Yes you can use Blairs formula for determining the distance of the baffle from the beginning of the exhaust port (using a generic beginning exhaust gas temp) but he didnt provide a formula for determining the change in exhaust gas temperature along the pipe length. So the distance comes out right for some engines but not for others.
One other old way of calculating the dimensions of an expansion chamber relied on generic formulas that put the emphasis on the wrong things. For instance pipe calculators would determine the belly diameter based on Blair's maximum size (2.5xheader dia.) and the header length based on a generic idea of length for engine type, and then let the diffuser be a byproduct of those two. The result was a disaster as anyone who has used them can tell you. The pipe builder would make a pipe as the program dictated and then chunk the lousy thing in the trash and try different dimensions till he found something he liked. The program creators had read and used some of Gordon Jennings generality statements while ignoring the fine points that Blair had written that make pipe making a thing of precision and not guesswork. How program makers could of overlooked the utmost importance of the timing of the waves in relation to the port timings is beyond me. But they did. The main bike factories make decent pipes for their bikes and so they either make and try 20 different pipes for each bike or they know the same tricks of the trade that I am sharing with you here. Any way now you can make a pipe that does what you want it to do. But, of course, if you want to stick to the old way you can. Sheet 1 of my Excel file uses formulas for its calculations but they should only be used as a starting point since the most accurate determination is after designing the diffuser and baffle and then looking at the combined return waves at sheet 3 in relation to port timing, and using the power grapher and then fine tune it from there.

I got sick of the silly free programs and the expensive "for sale" programs (and that waste-of-time 2 Stroke Wizard) and so made my own expansion chamber calculator spreadsheet. (Do it right by doing it yourself)

This screenshot is sheet 1 of 4 sheets: