My IROC has the stock heads and valvesprings and I know I need to upgrade them at the same time...whcih ones are direct replacement that will require no machining? Also my engine has 69,000 miles and the valveseals smoke at startup. Should I replace them at the same time or just have the heads completely gone thru? I think I know the answers here but would like your opinions just to make sure I'm right.

 

well i am a firm believer in doing it right the first time.i would replace the valve seals. and have the heads worked not that much more saves the haed ache of taking the heads off more than you have to. not an easy job as for you're valve train the maker of the cam should be ablt to tell you what you need.

 

I am pretty positive that the heads will most likely need to be cut at the valve guides to accomodate the .509 lift on the exhaust side of the ZZ4. There should be plenty stock diameter springs available. The question is what do you want to pay? If my memory is correct, LT4 hotcam springs are stock diameter and were not at all overpriced when I bought a set a few years back.