Honda Civic 2019 Manual page 33

Models with SPORT mode
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?
32
Unleaded gasoline with a pump octane number of 91 or higher
is recommended.
Use of lower octane gasoline can cause occasional metallic
knocking noise in the engine and will result in decreased engine
performance.
Use of gasoline with a pump octane less than 87 can lead to
engine damage.