Not shade tree at all. What you have to understand is that the mechanical advance and the vacuum advance over lap. The time you will here ping is at part load and WOT transition. The reason is because as the engine accelerates mechanical advance is advancing the timing, and at the same time vacuum advance is retarding it back down. If the springs are too light, the mechanical advance will come in too quickly and you will hear pinging. At this point, you go back one set of springs just like accel said.