I agree that 400 c.i. blocks don't overheat. Yes, the cylinder walls are siamezed. But, most people don't realize that 400 blocks require 400 heads to match the special "steam" holes in the 400 block. If lyou don't have 400 heads, then simply drill out steam holes in each head to match the block. And by the way, years ago this is precisely what Chevy recommended in their own Goodwrench high performance guide, complete with instructions on where to drill the holes in non-400 heads. I ran a 400 in my early corvette for years without the slightest hint of overheating.
