Horsepower difference ?

[Hib Halverson]

Originally Posted by A26B

That's because...... IF & When it does......... it Really is!
Referred to as catalyst reversion. (snip)

"Catalyst reversion"...LOL
More like "catalyst regurgitation."

I don't remember what Graham called it but he did explain that because of lower pressure in the cylinder, the engine sucked pieces of the cat substrate past the exhaust valve. I'd imagine, if that happens, the damage sometimes had to be more severe than just a broken oil ring. GM wouldn't have spent the money to redesign the exhaust manifold if it hadn't spent too mucy money on warranty for that.