In automotive engineering, a multi-valve engine is an internal combustion engine (4 stroke) where each cylinder has more than two valves. 4 valves engine can operate at higher rpm than 2 valves, providing high efficiency and more capacity. So 2 valves vs 4 valves, which one is better?
History of the valve engine
The first multi-valve engine appeared in 1912, in the Peugeot L76 Grand Prix racing car designed by Ernest Henry. It’s a two-cam and four-valve-per-cylinder (DOHC) engine. The 7.6-liter in-line 4-cylinder engine with a modern hemispherical combustion chamber produces 148 horsepower. Following that, many car manufacturers in turn also began to make multi-valve engines. Alfa Romeo (1914), Bentley (1921), Mercedes-Benz (1937)…
By the mid-1980s, 4-valve-per-cylinder engines became virtually standard on high-performance cars, such as the Ferrari 308 GTB Quattrovalvole (1982), BMW M635CSi (1983), Ferrari 288 GTO (1984), Mercedes 190E 2.3-16 (1984),…
What is 2 valves and 4 valves engine?
The name 2 valves already says that there are two valves at the top of the engine cylinder. 2 valves use air and fuel to generate power in the combustion chamber. The valve does the job of getting the right amount of air and fuel into the cylinder. 2 valves are used more in bicycle production.
Nowadays, most multi-valve engines use a 4-valve-per-cylinder design. This is the most common type of multi-valve engine with 2 exhaust valves and 2 intake valves alike. This design allows good intake and exhaust and since the small exhaust valves allow for high RPM. This design suits well for high power output.
Most 4-valve engines use double cams (DOHC) because of its obvious benefits, such as cross-flow intake/discharge, low inertia and friction, and also allowing for split intake and intake cams. independent discharge.
Which is better 4 valve or 2 valve?
Any four-stroke internal combustion engine needs at least 2 valves per cylinder: one for intake air/air conditioning, and the other for exhaust gas discharge. A small engine can use 2 valves. When it is at low speed, these 2 valves are enough to help the engine operate optimally. But at high speed, the opening and closing of 2 valves happens very quickly. Thus, it is not possible to ensure full carburetor and exhaust gas discharge. Moreover, if we keep increasing the size of 2 valves (increasing with cylinder size), the volume of these 2 valves will be large, but it also cannot achieve an optimal size.
Between 2 valves vs 4 valves, a 4-valve engine can overcome the disadvantages of a 2-valve engine that is to increase valve opening area. And, it improves intake and exhaust gas flow, thus enhancing combustion. efficiency, volumetric efficiency and capacity. The multi-valve geometry allows the spark plug to be ideally positioned in the combustion chamber for optimal flame propagation.
4-valve engines tend to have smaller valves hence lower displacement mass, preventing the valves from “drifting” out of their design position when the engine is running at high rpm thus allowing the engine to rev up. higher, which can reduce wear per cam lobe and allow more power from higher rpm without the risk of valve bouncing.
The downside, 4-valve engines use more components, so they weigh more and cost more. The early 4-valve engines weren’t known for their controllability. At low to medium rpm, they actually produce less torque than comparable 2-valve engines. Because the larger valve area results in slower air flow in the intake manifold. At low rpm, very slow airflow leads to imperfect fuel and air mixing, resulting in detonation and reduced power. For a race car or sports car, that might not be a big deal, but for regular passenger cars the lack of performance is considered unacceptable.
2 valves vs 4 valves motorcycle are quite common today. The configuration includes two large intake valves and two small exhaust valves. 4-valve engines are smaller in size and lighter in weight than 2-valves. They move freely and at higher frequencies, allowing the engine to run at higher rpm and provide higher efficiency.
Therefore, if you want to go long distances with an acceptable level of performance, at a cheap price, then a 2-valve engine will be the optimal choice. On the other hand, if you want to buy a car rich in torque and high performance, engine power,… then you should choose a 4-valve engine.
However, between 2 valves vs 4 valves, we will say that 4 valves is definitely better than 2 valves and now car manufacturing companies are trying to provide 4 valves for most of their motorcycles and cars.
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