Often hear the difference between two valve and four valve motorcycle engine, many riders ask, what does this mean? Is two valve good or four valve better?

Motorcycle engines generally have two-valve, three-valve, four-valve or even five-valve designs per cylinder. Here we discuss the difference between single-cylinder two-valve and four-valve.

We all know that the valve is a component that manages the intake and exhaust when the engine is working. When the engine is working, it is like a person running. The more valves, it means smoother breathing and higher efficiency of one-time inhalation and exhaust. Therefore, it also makes it easier for the engine to reach high speed, and high speed is the only way for the engine to increase power data. Therefore, the engine adopts a four-valve design, his high-speed performance tends to be better.

However, compared with the two-valve design, the four-valve design is not very helpful for the low-torque output at low and medium speeds. For the same displacement engine, the two-valve design will have smoother and more powerful output at low and medium speeds. For example, the GW250 engine uses a two-valve design per cylinder. The power characteristics pay more attention to low-torque output, but the maximum power is not large, only 18KW, high speed performance in general.

But not all four-valve design engines will be better than two-valve engines, this is not absolute. The power of the engine is generally closely related to the displacement, the number of cylinders, the cylinder diameter ratio, the compression ratio, and the maximum power output speed, and the number of valves mainly affects the last factor-the maximum power output speed. The four-valve design makes the engine intake and exhaust more efficient, and it is easier to reach high speeds.

Make it simple! Engines with four-valve design tend to breathe smoothly, are more suitable for the needs of high-speed engines, and have better high-speed performance, but the valve noise is often greater, the structure is more complicated, the volume of the cylinder head will be larger, and the cost will be higher. The two-valve design of the engine has a more timely low-torque response, can provide better power feedback at medium, low and high speeds, and the engine noise is relatively small, the fuel consumption is relatively low, the structure is simple and the cost is low, but the high-speed performance is generally not as good as the four-valve engine.

Some people may ask, since the two-valve engine is so good, but it is relatively weak at high speeds, why not increase the valve diameter, so that the four-valve intake and exhaust efficiency can be high? Well, it's a good idea, but it won't work either. The diameter of the valve can be increased, but at the same time the weight of the valve also goes up. The valve is reciprocating, and the vibration and noise will increase. You have to find a way to solve the problem of excessive vibration and noise. The loss outweighs the gain. The design of the engine is one link after another, and the overall balance is needed. It will not cause small losses to highlight a certain performance. Therefore, some high-performance engines often use light titanium alloy valves, which is the reason.

Therefore, the motorcycle engine uses several valves, which are completely the result of comprehensive measurement by engineers based on the performance positioning of the engine. Each has its own advantages and disadvantages. It cannot be said that who is more advanced and who is behind, mainly depends on which model is used. For small-displacement scooter models or cruise prince models that do not pay attention to high-speed performance, a single-cylinder two-valve engine is sufficient. For high-performance street cars, imitation races, off-road vehicles, etc., the four-valve engine is the first choice.