The fact people get wrong: the US/Canada M52 (1996-98 328i, 323i and 528i) has a cast-iron block, not aluminium.
Most other markets got the lightweight aluminium block with Nikasil-coated bores. BMW kept iron for North America specifically because high-sulfur US pump fuel attacked the Nikasil coating and caused compression loss — the famous Nikasil problem.
So a US-market 328i is iron-block; a European one is aluminium/Nikasil
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