What does motorcycle compression ratio mean?
2 Answers
Motorcycle compression ratio refers to the ratio of the total volume swept by the piston from top dead center to bottom dead center plus the combustion chamber volume, to the combustion chamber volume. The impact of compression ratio on motorcycles is as follows: High compression ratio: If the compression ratio is very high but low-grade fuel is used, it may cause knocking. Knocking occurs when the air-fuel mixture ignites prematurely before the spark plug fires, which is harmful to the engine. Low compression ratio: Using high-grade fuel in a low compression ratio engine can result in the air-fuel mixture not being compressed to an optimal point before ignition, leading to incomplete combustion, carbon buildup, and reduced power. Generally, a compression ratio of 10:1 can use 97-octane gasoline, while a lower compression ratio can use gasoline with a correspondingly lower octane rating.
I only figured out the compression ratio thing when I modified my motorcycle a couple of years ago. Simply put, it's how hard the piston squeezes in the cylinder. For example, 11:1 means the space above the piston is 11 times larger than the small space below when compressed. The higher the number, the more aggressive the compression, and the more explosive the power output—like those race bikes that rev up crazy fast. But the downside is it's more prone to knocking, so you gotta feed it premium 98-octane fuel to keep it happy. My daily commuter bike only has 9:1 compression, so regular 92-octane gas works fine, and I don't feel the pinch even in long fuel queues. If you're modding your ride, don't recklessly crank up the compression ratio—you might just punch a hole through your piston!
