from what Mike said it was real strange as to why some valves suffered horrible tulipping and others survived to live happier lives. I haven't personally had any issues other than the real early style 90s valves. We are using SI valves with good luck. The inconel from what I am told is too hard for the valves so a material that is "softer" works better with the metals in the valve. Just like the fix for the soft valve issue Nissan had, the fix was a softer valve. Good stuff man....