Two Stroke Design Software lists 6 Excel spreadsheets for designing/analyzing the following:
expansion chambers
head squish bands
crank balance
boost bottles
fuel/oil ratios
porting
So if you are really into DIY projects and want the most out of your 2 stroke then these may be of use to you. The crank balance calculator is for 4 strokes as well as 2 strokes. I made all these and the first one was because none of the free or cheap expansion chamber calculators gave anything more than moderate results. I was riding a 1 speed motorized bicycle at the time way up in the mountains and it was only a 49cc and I needed all the power from it possible so I made the calculator and made my own pipe that emphasized a long torquey powerband. It along with other mods turned my bike into a beast that would accelerate up hills. It was truly amazing. It also vibrated too much and I just guessed at the additional holes the crank wheels needed and drilled them with extra hard drill bits. It worked really well and later after making the crank balance calculator I saw that my guess was right on the money. Now I ride a 100cc 2 stroke street bike that has a half size reed valve and so the pre-powerband power dip is extra big and super annoying and the boost bottle took care of that because that is exactly what Yamaha designed for them to do. The Fuel/oil ratio calculator allows you to find the correct fuel/oil ratio based on the oils specs (viscosity, viscosity index, flash point temperature) instead of guessing or relying on what your hillbilly buddies use. The porting calculator tells you what the peak power RPM is for the exhaust port and for the transfers. The idea is that their PPRPM's should be fairly close to each other.