BMW: I have a 2002 BMW 325i with..., octane gasoline, 2002 bmw 325i

Question
I have a 2002 BMW 325i with 33,000 miles. Is harmful to the car if I fill the gas with grade 89 instead of recommended gas of grade 92? I have done it and did not notice any difference. Thanks!

Answer
Lena,

 If it were me, I would stay with 92 octane.  The lower octane gasoline may "detonate" early in your engine.  This causes spark knock.  Most new cars have a "knock sensor" that detects detonation, and retards the timing to prevent this.  Although you may not be having detonation, your engine will run with retarded ignition timing, and not reach it's full potential for HP/TQ.  
 I know the gas prices are high right now, but I would rather spend $.10 more per gallon, than have to worry about doing damage to my engine.  
 In summary, It is quite possible that you will suffer no effects from running 89 octane, but then again, I would not want to find out the hard way.

 Thank you for your question,
 Josh