what quality are the stock valves on an L03 engine? I am reading a book that is about building/modifying cylinder heads, cams and valvetrains. But, I figured these valves might be a little more tough than valves that would be on a regualar GM. But, if I'm wrong, let me know. I read that with heavy driving, it can realy heat up the exhaust valve and cause it to become very weak. So, are the stock valves capable of handling this sort of pressure on a stock or barely modified L03?