I wrote a little program a while back that figures piston speed, displacement, gearing, and helps you figure & track valve shimming.

Sure, you may say "Why bother, there's a ton of gearing and displacement calculators out there on the innerweb" and you'd be right.

This one's a little different, it has data for most popular quads preloaded :) -- and I just updated it with 06 TRX and YFZ info :D

http://www.xcracing.com/gabe/quad_calc.exe

You can run more than one instance of the program for handy comparisons....