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The four blade fans were also common on Early V8's from 1932 thru 1936 and there are thousands of those cars still on the road and they travel at higher speeds and RPMS than "A"s and there are no modern replacements other than the 6 blade plastic fans. These Early V8 folks don't seem to have too many issues with blades getting thrown thru radiators and hoods. Maybe the "A" people drive their cars too hard.