Octane rating won't harm or help your car either way. You will be fine to use either type in. (This is where someone asks why)
Why? Becuase all octane does is tweak the point of ignition for the air/fuel mixture.
Familiar with the R+M/2 method? In short, this is the method that gives the octane ratings based on a scale of 0 to 100.
On one end, 0, there is heptane, the other end, 100, being octane. Heptane will detonate under the slightest pressure. Octane you can compress to the point of hydrolocking and it will not detonate. The way the rating is determined is based on two tests: the MON (Motor Octane Number) and RON (Research Octane Method) your M and R, respectively. Test consists of a one cylinder engine that the lab will run at 900 RPM with an intake air temperature of 300 degrees F. Timing advance will be from 19-26 degrees. The lab will vary the compression of the engine as it's running looking for the engine to start knocking. Say they get the knock meter to read 20. The next step is to shut down the engine, then run it again with a known standard rating of gas, ISO-Octane at a 100 rating. The lab knows at what point the ISO will knock at, so they compare this to the 20 reading they got from the gas they are testing to get their first number, usually around 85 (The M in the equation). The perform the same setup again (using the Research Method), this time the engine running at 600 RPM with an intake air temp of 100 degrees F and an advance of 13 degrees. This produces a second number, usually around 93 (the R in the equation). R+M/2 = OCT ---> 93+85/2=89, so an 89 octane rated fuel.
So what's the point? The different octane ratings tell you how much the gas can be squeezed before it ignites, so a lower number is closer to heptane and will ignite sooner than a higher number, closer to octane, which has to be squeezed harder to get to ignite. Your engine's knock sensors will read the way the fuel is being ignited and adjust the ignition timing to suit. In cars that do not have knock sensors, you'll hear the knocking or pinging, as the engine won't compensate for it.
MYTH: Higher octane give me better gas milage
FACT: Using lower octane rated fuel in a car that is designed for higher octane AND HAS KNOCK SENSORS will seem like it's getting worse gas milage because the lower octane fuel will make the car retard it's timing to compensate. This translates to less milage, as you are going to push the pedal a little farther to get the same effect.
This brings us to
MYTH: I get more power with high octane
FACT: Same as above, really. When you use the proper octane rated fuel for your car, your car will be running at optimum timing and delivery, etc, seeming like a boost in power you're just not pushing the pedal as far to get the same performance as a lower octane. It's not the gas thats causing the lag, it's the computer, and you.
This said, it doesn't matter one bit which octane you use, as far as harming the car goes. Make sense?
