"Does a chip or tune actually do anything on the US S52 M3?" — the realistic answer: on a naturally-aspirated S52 (or M50/M52), a software tune gives modest gains by cleaning up fuelling/timing and raising limits, but NA power comes from airflow (hardware), not software. Don't expect turbo-car "+40 hp from a flash" numbers on an NA engine. See S52 Detuned Myth and NA Boltons Worth
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