gasoline octane requirements

tomsrtomsr Member Posts: 325
edited April 2014 in Acura
I just bought a new car and the owners manual says
91 octane is required.My son works for this particular dealership and says they routinely use
89 octane.Looking at various car magasines I see that a 10:1 compression ratio calls for premium fuel.My car has a 9.8:1 ratio.If I see no noticeable performance difference will I harm the engine over time using 89 octane.I don't drive in the mountains,tow anything,or drive over 70 mph.


  • blackgtpblackgtp Member Posts: 19
    You did not mention the model of car you bought but my guess would be that the owners manual might say that 87 octane or better is acceptable if premium fuel is not available.

    For the most part, the lower octane may cause a spark knock that the knock sensors will pick up. This will cause the computer to retard the timing thus reducing power and eliminating the knock at that time. Mild brief spark knock will generally not hurt anything but heavy continuous knocking will cause damage.

    You probably bought the car because you liked the performance among other things. If the engine was designed for high octane, then I say use it or buy something else. The dealership saves money using 89 octane in cars that are at the dealership for a short time.
  • armtdmarmtdm Member Posts: 2,057
    Yea, most salesmen will also inform the buyer that 87 is fine but most of these idiots have never read the manual on the car they are selling either. They don't know if the engine has a chain or a belt or any service requirements. they just sell cars. Plus, dealers cut cost and one way to do that is use cheaper gas!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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