Acura ILX 2021 Owner's Manual page 29

Unleaded gasoline with a
Pump Octane Number
(PON) of 91 or higher is
recommended.
Is it possible to use
unleaded gasoline with a
Pump Octane Number
(PON) of 87 or lower on
this vehicle?
Use of a lower octane gasoline can cause occasional metallic
knocking noise in the engine and will result in decreased engine
performance.
Use of a gasoline with a pump octane less than 87 can lead to
engine damage.
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