Horsepower difference ?

[A26B]

Originally Posted by Hib Halverson

"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.

For sure! This ring isn't broken. The lands have been completely eroded away. The cylinder liner was toast & piston badly scored. I just don't have photos of the other components. The damage wasn't confined to just a single cylinder.

In chats with Chris Allen & Graham, I don't recall this problem being associated with the few warranty returns. Maybe so, I just can't say.

My perspective on the manifold re-design and fabrication experience. Separating the converter from the manifold is a win-win. Simpler to manufacture & a lot less costly to replace a bad catalytic converter, in terms of both labor and components.