I also don't know what I don't know. Kinda makes sense. I think. One of the things I set about getting a handle on this year was making sure my pushrods were the proper length. Trying to measure actual valve lift with the engine in the car was always a struggle. I was of the opinion I was giving up .030" of lift. After poring over a few treatises on pushrod length and rocker geometry (none of which made acertain light bulb go off like BradH's diagram), I have determined that I'm within .020" of optimum pushrod length. Can't really say that's worth buying new pushrods for my heap. Actual valve lift is within .005 of theoretical so...