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Message: <blockquote data-quote="shovel" data-source="post: 1543548" data-attributes="member: 29855">If you have the stock heads then your compression ratio is 9:1 and you could run Euro 90 (US 87) at sea level without a worry in the world.    If you aren't running forced induction or increasing your compression ratio there isn't much you can do to deliberately take advantage of a higher octane fuel.   You will have more freedom to adjust timing with a more stable fuel but the performance value of doing that with a compression ratio of 9 and above sea level is negligible.   If you tuned rich and advanced the base timing a degree or three you might see some WOT power but you'd also be depositing a lot of soot on your oxygen sensors, cats and EGR valve which doesn't strike me as a long term strategy worth hunting.  If you greatly increased aspiration (performance heads, cam, intake manifold) then you'd be filling the cylinders with more air and even with the same compression ratio you'd want to run a little more advance.   Flames travel faster in denser air so you start the fire earlier.   A higher octane fuel would allow that to happen just right in a wider range of temperatures and throttle positions without knock.</blockquote>