Should the older GL8 use 92 or 95 octane gasoline?

[LeTalia]

According to the official vehicle manual recommendation, the older GL8 should use 95 octane gasoline. In addition to checking the appropriate gasoline grade in the vehicle manual for the older GL8, you can also find it indicated on the fuel tank cap. Typically, the gasoline grade can also be determined based on the engine's compression ratio. Vehicles with an engine compression ratio between 8.6-9.9 should use 92 octane gasoline, while those with a compression ratio between 10.0-11.5 should use 95 octane gasoline. However, with the application of some new technologies nowadays, the gasoline grade cannot be solely determined by the compression ratio. A high compression ratio can also be tuned to use lower octane gasoline. This is because, besides the compression ratio, other factors such as ignition timing, turbocharging technology, and Atkinson cycle technology also play a role. Generally, the higher the gasoline grade, the higher the octane number and the better the anti-knock performance. 92 octane gasoline contains 92% isooctane and 8% n-heptane, while 95 octane gasoline contains 95% isooctane and 5% n-heptane. If the older GL8 occasionally uses the wrong gasoline grade, simply switch back to the correct grade after use. However, long-term use of the wrong gasoline grade can have the following effects: For vehicles recommended to use lower octane gasoline, using higher octane gasoline will not cause damage, but the increase in octane number will change the fuel's ignition point, leading to delayed combustion in the engine. This means both the engine's power output and thermal efficiency will decrease, resulting in poorer performance in practice. For vehicles recommended to use higher octane gasoline, using lower octane gasoline can cause engine knocking. Because the octane number is too low, the gasoline's ignition point decreases, causing it to ignite prematurely during the compression stroke. If the fuel ignites before the spark plug fires during the compression stroke, resistance will occur during the upward stroke. This resistance will make the engine run very unstably. If the knocking is imperceptible, it only increases noise without obvious damage to the engine. However, if noticeable knocking occurs, it indicates severe engine conditions, affecting not only driving stability but also causing abnormal wear on pistons and cylinders, and in severe cases, cylinder scoring.