I dare say that most of the engine problems were cause by the drivers. Back in the old days, the L78 solid lifter engines were known to drop valves on more than a few occasions. The problem seemed to be lack of valve spring pressure. Just switching to the heavier L88 springs seemed to cure the valve float problem. In those cases, the valve was not keeping up with the rest of the valve train and was actually free falling shut, eventually pounding the keepers through the retainers. Might just be the same problem here when guys try the wild rpm thing. Just a thought. A friend of mine who has raced for years is paranoid about having enough spring pressure for the rpm he intends to turn. He never drops valves.