Just got done talking to a friend who bought big block Pro Comp heads 10 years ago and had a valve failure with both the intake and exhaust in one cylinder at probably 7K at the big end of the track... (134mph) Took out his big block Stroker.. he put new valves in it when he rebuilt the motor and still has them to this day. Just isn't convinced the hardware was very good.. so I guess the question remains whether that was then or that's how it always will be..???..