It will depend on how they will be used. We buy them bare (do not buy them if they have PC parts in them) and check them here in our shop. Some we will have to do valve jobs on and others are ok. Sometimes you will find that the guides are too tight. Over time, we have found out that if you use good parts they have been pretty good. I have a customer that has a set of the CNC 360's on a 525 in a dragster that runs 4.80's in the 1/8th. I probably wouldn't use them on a blown application.lol