That's false. The octane (itself) has nothing to do with burn rate. As a good example, Sunoco SR18 (118 octane) has a faster burn rate than 93 octane pump fuel.
Higher octane simply means a longer timeframe before auto-ignition of the end gas occurs which is not related to the flame speed.
The resistance to combustion (burning in the engine) is what keeps high octane fuel from causing knock and ping. Fuel is burning too quickly, early in the combustion cycle, when you have knock/ ping. High octane fuel keeps this from occurring.
I will edit it causes the back of exhaust valves to get covered with carbon, potentially, because premium/high octane air/fuel mixture combusts slower in the engine and if the engine isn't designed for premium you potentially have that issue due to the fuel finishing its burn as the exhaust valves are further into opening. The spark ignites the fuel at the same time whether it's high octane or lower octane. It's how long it takes the fuel to combust from that point that is whether you get undesireable results or not.
Last edited: