....will cause the (same) hammer to hit the valve traveling faster
Hi Scott, I did an experiment once where I made up a number of spacers in .005 increments, that I placed on the back of a valve to see what different dwell times would do. On this valve using a .070 spacer I got a noticeably higher velocity, than with a .005 thicker or thinner spacer. It was a sweet spot for velocity. I was surprised by how narrow the spot was. Maybe you were hitting it with your minor hammer stroke and weight changes?