The only problem I’ve seen out of the stealth heads is the deck need some work. My shop refused to install ANY alum heads without checking the deck for straighteness. He had a set of stealths start to leak compression and loose power on the dyno. It took .004 cut the straighten them out. Sure enough when he cut mine, it took .004 to fix the problem on both heads. The were both low in between the two middle chambers. He always cuts ANY brand of alum head. He’s just seen issues with alum heads for some reason. I cleaned up the bowls and lapped the valves in mine and they looked fine. Guides were fine as well.