Recently, a gas station that sells non-ethanol gasoline took over the location of another gasoline retailer in my neighborhood. The old retailer did not sell Top Tier gasoline. The new retailer sells Top Tier gasoline. The new retailer also sells non-ethanol Top Tier gasoline, but only in 89 octane. Should I continue using the 92 octane with 10% ethanol or should I switch to the 89 octane non-ethanol gasoline? Both would be Top Tier gasoline. Which would be better for the Cayman?
Octane does not "boost" performance; it simply makes combustion happen at a higher temperature. When you compress a fluid (like fuel), it makes it hotter--just physics. The engines in Caymans have an 11:1 compression ratio--higher than a "normal" engine. That is the reason they require the higher octane.
So, the ONLY reason to use 93 octane is if you need to to prevent early (before the spark) combustion. Early combustion can cause damage to your engine! That said, many newer cars, like Caymans, will automatically advance the timing, when using 89 octane, to prevent damage, but the cost is in performance due to the fact that the timing is not optimal.
On the flip side, if you have a Honda Civic, 93 octane will do NOTHING (except cost you more money) because the engine has a lower compression ratio.
And as a previous reply said, ethanol gives you a little worse gas milage because it has less carbon in it, but newer cars are made for it. Octane and ethanol are two completely different things--not even comparable.
If you want LESS performance in your SPORTS CAR and nominally better gas milage, use the 89 octane, ethenol-free. Otherwise, stick with the 93 octane, 10% ethenol.
