hornet7288;2058979 said:
Chrome rings have a low tolerance for dirty conditions like dirty oil or air. They take heavy and constant stress better and last a long time, but they should only be used in fresh bore or hone jobs.
Moly rings should still be used in cylinders that have a fresh bore or hone since the grooves that are in the cylinder where made by the previous rings and will only seat properly to those rings.
Iron rings can be used in "used" cylinders but I wouldn't recommend that since you could loose compression and contaminate the oil. Personally I would go the moly route since chrome needs to be specially bored or honed to accommodate the rings.