Has anyone ever figured out why these heads crack? Is there any correlation between plenum failure and head damage?

 

They are poorly cast. Plenum has nothing to do with it.

 

Not entirely true, the plenum fails which leads to burning oil which leads to clogged cat which leads to cracked heads.

 

The heads can crack even without the blown plenum. They were just **** poor castings, decks were too thin. There are better heads available in the aftermarket, for under 300 a pop.

 

So additional oil leaking into the air intake would also cause undo hydro compression on the heads, assisting with the stress?

 

Nah, the burning oil clogs the cat, so cylinder temps go up... making cracks more likely.

 

I knew there were several theories out there, clogged cat, bad castings.. so I just wanted the pro's takes

 

Just blame George Bush.

 

LOL Which one?! So many to choose from.. and so much blame to go around.

 

Lets chase this rabbit down the hole even further.

Clogged cat, leads to higher cylinder temps, leads to higher exhaust temps, leads to cracked exhaust manifolds or leaky gaskets, which leads to a slight amount of winter air to go in through the leak before the compression cycle, which is too cold and makes the exhaust valve crack....