I was calling read. I suspect the real problem is explained by another commenter, who points out that 80 MB of ASCII text will become 240MB of UTF32 in the hand

I was calling read. I suspect the real problem is explained by another commenter, who points out that 80 MB of ASCII text will become 240MB of UTF32 in the hands of SBCL, not to mention all the additional words of memory required for cons cells.