Authoritative nomenclature from BillG993/bmdaia level expertise: (1) 'The Mezger' — all flat-6 air-cooled short blocks derived from Hans Mezger's 908 crankcase (1963-1998); (2) 'Group-C Mezger' — Mezgers with water-cooled heads (1978-2015), 930 crankcase; (3) 'GT1-Block Group-C Mezger' — 9R crankcase. All three are air-cooled by definition (the short block is air-cooled; only the heads on Group-C variants are water-cooled). …
Mezger nomenclature — three classifications by crankcase
Porsche 911 (997) · factory-spec