91 octane fuel has more potential power than 87 octane fuel. Any gasoline engine will efficiently burn any octane fuel. The engine's compression ratio is the most important factor in selecting gasoline octane. Posted fuel octane ratings are a result of testing fuel in the laboratory and under actual operating conditions. Diesel engines require a low octane fuel.
Engine knock or ping is always a result of poor quality fuel.
Gasolines are seasonally and regionally blended. This is an important energy saving activity for students. Most vehicle owners never refer to their Owner's Manual to determine the acceptable octane fuel for their vehicle. It is true that excessive and continued pinging and knocking is harmful to an engine and this MUST be attended to immediately or serious engine damage will result. Very few recently manufactured vehicles require premium, high octane fuel.