Diamonds are based on the late '31 production motor and have heavier rear main reinforcements. They are (or may be--accounts vary) heavier than regular blocks by several pounds, so may have extra metal elsewhere. The diamond mark is just behind the flange where the front cover bolts on near top of passenger side of block. At bottom edge of block, also right front, is a cast in date mark. The diamond is only about 1/2" long and is faint enough to be obscured by heavy paint. I was searching the swap meets for a diamond B motor last year. One evening my flashlight slipped as I was tinkering with the fuel pump and the angled beam suddenly brought out the nearly painted over date stamp--my '32 pickup already contained a good running diamond!

Diamond heads also have a date casting that doesn't exist on production blocks, and allegedly have slightly smaller chambers than standard. I haven't had an opportunity to check this.

There is lots of info on diamond blocks in the Secrets of Speed journal, much of it contradictory...

The bottom line is that no one really seems to know a lot about these. I believe that the advantages are at best minimal, but they are a cool and esoteric distinction for an old banger. Bruce



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