Basically drilling pistons decreases the pack, the pack is the amount of force needed to increase the damping due to pressures in the oil, by increasing pack this happens at higher shock speeds so the small bumps are soaked up as well as the big ones because you also use thicker oil. It's hard to grasp I know but imagine the piston as two chambers with a pressure regualator in between them it only lets through a certain amount so when the shock piston travels slowly the pressure only increases at the top a little bit but when it goes faster the pressure increases much more stopping the car bottoming out as easily but if you do this with the same wt oil it just goes straight through those huge holes so you use stronger oil if you did it in reverse i.e small holes thick oil then you are going to have a really firm ride and it's going to bounce around one hell of a lot and not get much grip. I have a guide that shows all of the tuning factors and explains them really simply with examples of what kind of track it is good for if you PM me your mail I can send it, if you want it[8D]