In the U.S. at low altitude for low compression ratio vehicles, defined 87 octane gasoline is standard. However, most gasolines use a mix(E10), with 10% ethanol(114 octane). To have the designed 87 octane, the gasoline making up 90% of the fuel, must average 84 octane. So if there is knocking, its the 84octane gasoline. Switching to 100% ethanol-free 87 octane gasoline(E0), ALL the gasoline molecules average 87 octane & your knocking should quit. Also, since the 114 octane ethanol is in an 87octane designed engine, the ethanol is missing much of the power stroke of the engine. Thus, in my last 5 low compression ratio 87 octane engines, MPG of E0 compared to E10 increased 8%, 8%, 7%-8%, 7%, & 5%, just be eliminating the 10% ethanol. Almost always, E0 was considerably more expensive than E10, altho up to 5 years ago, I could find E0 for only pennies more expensive than E10. That is no longer true & E0 in our locality is 90+ cents more expensive than E10.

Here in Scotland all fuel is 5% Ethanol. No other option available.