no need to be be persuaded by everyone who claims higher octane is a wonder drug for our cars. more power, more reliability, engine longevity blah blah blah......it was designed to run on 87, LOTS of people run it with no issues. Run whatever makes you feel good.
I've run 87 for 5000km and have run 91 for the next 5000km (first 10k of the cars life) and i really didn't notice a difference. Going to switch back to 87 again and observe driveability and mileage some more and see if it changes. My mileage seemed a bit better with 91, which has no ethanol in my area while most of the 87 has "up to 10%" ethanol as posted on the pumps. The difference isn't worth the extra price if we are talking purely about dollars and cents, if it was even due to the fuel.
The difference is in:
1. knock. Octane is a measure of the fuel's resistance to knock. Lower octane equals more knock - that's a fact. GDI motors are prone to knock - also a fact. Turbocharged GDI motors are even more prone to knock as well as "super knock" (i.e. LSPI) which can cause catastrophic failure - also a fact. The ES uses an adaptive ECU, meaning it can change operating parameters, including timing, on the fly - fact. This ECU will retard timing when it detects knock - fact.
2. carbon deposits. Because these are GDI motors, no fuel washes over the intake valves - fact. Because no fuel washes over the intake valves they don't get cleaned the way they do in non-GDI motors, so carbon deposits will build up far faster on the intake valves in a GDI car compared to a non-GDI car - fact. Higher octane fuel will leave fewer carbon deposits on the intake valves - fact. Eventually carbon deposits will cause the intake valves to not seat/seal properly during combustion, robbing the car of power over time - fact.
It's not a wonder drug - no one is claiming that it is. However, it most definitely helps with engine longevity and power delivery.
The car isn't "designed to run on 87". It can
run on 87, but that is simply the minimum octane rating recommended by the manufacturer. It will absolutely run more efficiently on higher octanes.