I've always driven trucks with poor mpg so never really considered anything above 87 octane fuel. However, I'm considering switching to 91 for this car. It would only be a few more bucks per fill up and when I think how often I spend a couple bucks w/o a second thought I'm thinking, "why not"? Any real world benefit to running higher octane or am I just throwing money away? What are you running? If you have a gas station preference, please list that as well.
This motor is tuned for 87 Octane, from what I understand.
Octane is bad. Why? All it really is is an impurity introduced to the fuel to make it harder to ignite, so that it won't combust before the piston is at the bottom (or top, depending on your concept) of its stroke and the spark fires. If this were to happen in mild cases, it would unbalance the engine harmonics, and you would GREATLY increase wear, lose power, etc. Modern vehicles have variable timing and the computer senses minute harmonics changes and retards this timing, so as to accommodate sub-par fuel. This causes a loss in power. In the 2015 Mustang GT, 87 octane is a programmed fuel map, with 91 octane preferred. You lose roughly 15 horsepower to your cheapness, if you run 87. This is on a 400+ horsepower 5.0L V8. On older vehicles, you just lost efficiency and the motor died sooner rather than later. In extreme cases, a piston would fracture or peel like an onion or the flame-front would be more focused and burn a hole straight through it. All "one and done" type failures. Newer cars, as I said, just pull timing and you motor on blissfully unaware that you are narrowly avoiding catastrophe, and probably not noticing the few hp you lose, anyway.
But...these engines were designed to function properly on 87 octane. 87 octane has a higher potential energy (due to less impurity). 87 Octane is cheaper. 91 octane won't cause the ECU to give you any more timing advance than 87 will, if the system is optimized for 87 octane. So...DO NOT use 89+. It's a waste of money.
Now...if Mazda "lied" and the ECU is very adaptive and simply adds timing until pre-knock is detected and them backs off a touch...yeah, then the highest octane you can buy is the most effective solution. However, I somehow just don't think they did this. Call it a hunch.
