Using higher octane gas than suggested

[who?]

My 2006 Focus manual says the engine has a 10.1 to 1 compression ratio but recommends 87 octane. It does recommend against using 86 octane regular at higher altitudes.

 

[Zenmervolt]

My 2006 Focus manual says the engine has a 10.1 to 1 compression ratio but recommends 87 octane. It does recommend against using 86 octane regular at higher altitudes.

As engine design has gotten better (especially with computer simulations of combustion chamber temperature characteristics) higher compression for a given octane rating has become possible thanks to a reduction in hot spots that could trigger pre-ignition.

ZV