What do bore and stroke mean?
2 Answers
Bore refers to the diameter of the cylinder, while stroke is the distance between the top dead center and bottom dead center of the piston movement. Below is relevant information about the stroke-to-bore ratio: 1. Definition: The stroke-to-bore ratio is the most fundamental and critical structural parameter of an internal combustion engine. It not only significantly impacts scavenging efficiency and heat transfer but also affects engine power and fuel consumption rate. Additionally, it influences the structure and dimensions of all components, thereby affecting engine vibration, specific weight indicators, and service life. 2. Ratio: If S/D is relatively large, the volume occupied by residual exhaust gases in the cylinder increases, along with greater scavenging resistance. This results in a longer path for the fresh air-fuel mixture during the scavenging process, inevitably leading to mixing with exhaust gases and reducing scavenging quality. A larger S/D also increases the cylinder's surface area, leading to greater heat loss.
When I first got into cars, a friend at the repair shop explained the meanings of bore and stroke to me. Bore refers to the inner diameter of the cylinder, or the diameter width of the piston's movement, usually a circular dimension. For example, common family cars might have a bore of around 80mm. Stroke is the distance the piston moves up and down in the cylinder, the length from the highest point to the lowest point. These two numbers can be used to calculate the engine displacement with a simple formula: bore squared multiplied by stroke, multiplied by a coefficient, and then by the number of cylinders. For instance, engines with a larger bore, like those in some sports cars, often have higher RPMs and more powerful performance. Engines with a longer stroke, like those in SUVs, provide strong low-end torque, making them better for hauling loads. Understanding this can help you choose a car that better suits your driving style—shorter strokes are more fuel-efficient for stop-and-go city driving, while larger bores offer quicker acceleration on highways. When modifying, pay attention to balancing these parameters; don’t just chase power at the expense of reliability.
