[Sirrotica]

My experience is with a 65 GTO, 389 that was naturally aspirated that ended up with a piston inside of the water jacket when the cylinder wall collapsed. After that experience I would never recommend someone use one of those blocks for a supercharged application. Pontiac had warranty claims back then due to failed blocks due to their "Thin wall casting process". which covered 65, and 66, 389 engines.

Put new pistons in one of those blocks would usually include boring the engine, further weakening the cylinder walls. Mine was bored, with forged pistons, and at roughly 3000 RPM the cylinder wall just collapsed, completely destroying the engine. I was just cruising along when it happened.

The earlier 389 blocks had much more beef in them than the 65, and 66 blocks did. Anyone else that would recommend using a 66 block, probably didn't have the same experience I had. It is fairly well known that those 2 years had thin cylinder walls, I read about it after mine failed in one of the monthly car enthusiast magazines back in 1971, too late for me though.