Any aftermarket head, from any manufacturer, for any manufacturer, should be taken to a reputable performance shop and gone through. That means the valve job gets redone because the guides are usually tight, the seats are not really round, and the valve grinding isn't the best, the deck surfaces might need surfacing (if you are running MLS head gaskets), and the right springs added for your cam because you can't go by lift alone... The supplied springs are not that good especially for a modern cam profile. Indys are no better. Stealths are no better. Anybody who spends the coin for a decent set of heads should spend the few more coins to get the maximum performance from them. Core shift is common in any cast product. It's faster and easier to just take care of it then send it back and *****. It's not like you're grinding aluminum.
