No, don't use premium!
The octane has nothing to do with energy content of the gasoline. It is a measure of how hard it is to ignite and how fast it burns. Your engine will run better on the proper octane than on either too low or too high an octane.
High octane burns fast, and it is hard to ignite. The pistons are moving at a particular speed. There is a pressure curve on the fuel burn, which starts out at zero then goes up to a peak, then comes back down. In a perfect world the piston would be moving at the same speed as the fuel burns so that the pressure pushes for the longest time on the piston. A longer firm push transmits more energy more efficiently than a single fast impulse. Work done is force applied multiplied by the distance. You get more work (energy) out of the gas if the pressure wave matches piston speed.
Detonation is an engine killer, and happens if you run too low an octane. Detonation tends to happen at high throttle, meaning you are letting a lot of air and fuel into the cylinder, and it happens at lower rpm. So, if you are not running at full throttle and not demanding a lot of power, you could in fact safely run a lower octane in your engine and get more efficiency out of it. However this is not practical because you never know when you'll have to (or want to) demand more power. But the lesson is that the most efficient (powerful) burn of fuel is with the minimum octane required to avoid detonation. The engineers who designed the engine will build in some buffer, which means the recommended 87 octane is safe and is the most efficient fuel choice.
Ethanol-free gas will contain about 7% more energy than 10% ethanol. I get about 5% better fuel economy in my car and my V650 when I burn it. The cost here is right around 5% more, so I buy it when it is convenient, just to reduce how frequently I have to buy gas. But the same rules apply for octane, don't bother with higher octane just to get the non-ethanol.
Last edited by Fly-Sig; 07-26-2019 at 12:48 PM.