has anyone had valve guides collapse and break up on an 20 xe head im running NOS n have suspision its not running right or not set up right hense the engine being scrapped. The guides look like they have broken up on the exhaust side and the inlet?? which has left me stumped as i thought if it was the NOS it would just burn up the exhaust valves if set up wrong and iv never heard of valve guides breaking up b4. Its not a coscast head and yes i now have an xe with piston tops like an artexed celiing in your house gutted.anyone know what might have caused it??