Compression Ratio 9.5:1 - What Grade of Gasoline to Use?

[Myron]

If the engine's compression ratio is 9.5:1, it is recommended to use 95-octane gasoline. Engines with a compression ratio above 9 should generally use 95-octane fuel, as higher compression ratios typically require higher-octane gasoline. Below is relevant information about the relationship between compression ratio and gasoline grades: The correlation between compression ratio and gasoline grades: The primary basis for selecting gasoline grades is the engine's compression ratio, because the air-fuel mixture generates heat during compression - the greater the cylinder pressure, the higher the temperature becomes. For example, engines with compression ratios below 8 can use 90-octane gasoline. Gasoline's anti-knock properties: After the air-fuel mixture enters the cylinder, the piston moves upward to compress the mixture. As pressure increases, temperature rises sharply. If the gasoline's anti-knock properties are insufficient, combustion may begin spontaneously before spark plug ignition, causing engine knocking. A vehicle's compression ratio represents the ratio between the cylinder's maximum volume at bottom dead center and minimum volume at top dead center during the compression stroke. Gasoline octane rating indicates the fuel's actual anti-knock performance relative to standard gasoline. Higher octane numbers indicate stronger anti-knock capabilities.