Also for note, because the exhaust is open on a 2-stroke for most of the actual compression stroke they have a seperet rating called corrected compression ratio, which is the volume of the combustion chamber at TDC divided by the volume in the cylinder when the exhaust port is closed. But it all kind of goes to hell with a pipe anyways due to the charging effect of the waves. I've read that some scooter race kits run as high as 15.8:1 but they also have an exhaust duration of about 190 degrees, and only do about 140 psi, on the stand with me kicking it, the pipe will make it much higher at running speeds. Also read that a 125cc with a proper pipe can have as much as 144cc of gas in it due to the pipe, (something like that).