Ok what is a siamese block. I think i know but really aint sure. Please someone let me know.

Thanks,
Derek

 

With Siamesed bores, there is no water jacket where the bores are closest together; the casting is continuous and there is a solid wall between adjacent bores. They are "conjoined". Non-Siamesed bores have water completely around each cylinder wall.

FWIW: "Siamesed" comes from "Siamese twins". The first pair of conjoined twins of any prominence (c. 1811) were Chang and Eng who were joined at the abdomen and shared a liver. They were originally from Siam, now known as Thailand, hence the name. ("Thailandese twins" is too hard to say. )

Siamesed bores are conjoined and are therefore stronger, especially for large bores, like 4.125 and above in a SBC with 4.400 center to center bore distance. The conjoined bores distort less so they can theoretically support more power. The downside is that cooling water doesn't get to that conjoined area so more heat is retained in the cylinder walls, and perhaps distortion could be more because the wall thickness and support varies greatly around the bore. IMO, for large bore-to-bore spacing ratios (like 4.125+ in a SBC), conjoined bores are the best choice.

 

The Gen1 small block 400ci is a siamesed block. They were notorious for blown head gaskets, cracked head or block if they overheated. I broke one myself in a 74 chevelle malibu. I have to say it's somewhat peoples own fault. If they got too hot you should just pullover and let cool. Trouble came when you tried to eek a couple extra miles with it hot and they wouldn't tolerate it.