M103s don't have knock sensors, and will rattle, ditto for M117/M119 early with K-jet.

Play it safe, use premium. Detonation at high speed, when you cannot hear it, will roast the piston crowns and valves, not cheap.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!