lack of power on 280e euro

[harvey chupin]

Recently bought 1980 280e euro with manual transmission. The specs say it should have 182 bhp but it certainly doesn't feel like it. What adjustments are exactly made to an engine of a grey market car like this? This one arrived to US 5 years after it was bought brand new in Germany.
Do they retard or replace cams, adjust ignition timing or replace sparkplugs or more? The car was made for 98 octane gas consumption widely used in Europe at that time. It was pinging so my mechanic adjusted ignition timing (advanced or retarded, not sure) and it was gone, having a smoother ride and more power at low rpm. It still feels like it needs more power though.
What can I do to get back the original 182 bhp(without putting in super chargers, etc.) or is it just impossible because of the low octane gasoline here in the US? Can I advance cam timing by simply adjusting timing gear?

Thanks.