I've got a 67 Dodge Dart with a 383. Last fall I broke a valve right at the keeper. I was wondering what caused this? I have had a few people tell me bad valve springs can cause this but I had them pressure checked and they checked out to speck. Prior to the valve braking it would stop pulling in first or second gear around 5000 rpm. Never both gears which was weird. Which would remind you of a valve spring problem. So I need to get the head fix but am afraid of this happening again. Fortunately it didn't hurt the short block this time.