What Grade of Gasoline Should Be Used for a Compression Ratio of 9.1:1?
2 Answers
For a compression ratio of 9.1:1, 95-octane gasoline should be used. Compression Ratio: It indicates the degree to which the gas in the cylinder is compressed when the piston moves from the bottom dead center to the top dead center. The compression ratio is one of the important parameters of an engine. For modern automotive engines, the compression ratio of gasoline engines is generally 8-11 due to the limitation of knocking, while diesel engines, which are not limited by knocking, typically have a compression ratio of 12-22. Effects of Compression Ratio: The compression ratio should neither be too high nor too low; the most important thing is to keep it within an appropriate range. A higher compression ratio results in greater output power, whereas a lower compression ratio leads to smaller output power. However, a higher compression ratio is not always better. An excessively high compression ratio is usually accompanied by significantly increased engine vibration during operation. When it exceeds a certain value, it can cause engine overheating, reduced power, increased fuel consumption, and even engine damage. On the other hand, when the compression ratio is too low, the most obvious characteristic is insufficient engine power.
As an enthusiast who frequently tinkers with my old car, a compression ratio of 9.1:1 falls into the medium-high range for me. I recommend using 95 or 97 octane gasoline to avoid issues. For example, my first car had a compression ratio of 9.2:1. Initially, to save money, I used 89 octane gasoline, but soon the engine started making knocking sounds—that's detonation, which means abnormal combustion of gasoline, damaging the internal cylinders. After inspection, the mechanic said that if the compression ratio exceeds 8.5, you need to use higher octane gasoline; the octane value must be high enough to withstand high-pressure combustion. Later, I switched to 97 octane gasoline, and the fuel consumption stabilized noticeably, with the engine running much smoother. Actually, the relationship between compression ratio and gasoline octane is significant: using low-octane gasoline with a high compression ratio can easily cause pre-ignition and engine overheating, and in severe cases, it can even reduce engine lifespan. Therefore, I always advise new car owners not to skimp on small savings—check your car's user manual. Generally, manufacturers specify the appropriate octane rating, which is both worry-free and safe.
