59 block questions

[38 coupe]

Originally Posted by Bored&Stroked

Interesting that the letter mentions that SAME block for the entire 59x series. What has been common belief is that the 221 (90 HP blocks) had thinner cylinder walls that the 239 (100 hp blocks). I've heard for 40+ years that you had to be careful trying to bore a 221 CI 59X block due to thinner walls - that they wouldn't support a 3 3/8" bore. The above letter refutes that - claiming they're all the same. What we don't know is if the foundries all used the same patterns/core boxes or not.

Anybody have any first-hand sonic test experience with the 3 1/16 221 blocks? I've never built one?

I suspect the foundry did their own thing and made blocks using existing 221 cores. How else do you explain the 59 blocks that pass the pencil test? I also expect a few of the blocks did use the regular 59 cylinder cores and can be bored big, but that probably wasn't typical.