I would not recommend using a lower octane rating than your car requires.

Ever.

Should you do so, your engine's anti-knock sensor will retard the timing to prevent detonation, which can damage the piston crown.

Retarding your engine's timing robs your engine of power, negating any benefit you might be trying to achieve.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".