SOHC vs. DOHC: What’s the Difference?
Before we get into the distinctions between a SOHC (Single Overhead Camshaft) and DOHC (Dual Overhead Camshaft) settings, let’s first clarify what a Camshaft does. A Camshaft is a cylindrically shaped rod with a bunch of oblong lobes that extend from it within an internal combustion engine (whether it is air-cooled, oil-cooled, or liquid-cooled). For each spin, the lobes force the intake valve(s) to suck air within the cylinder to combine with gasoline and combust, and afterwards, the exhaust valve(s) to let the arising vapours exit. This makes the engine run. Now let’s understand what is the difference between SOHC and DOHC.
A SOHC arrangement generally allows for two or three valves per cylinder, with one valve allowing air to enter and the other allowing vapours to exit. Nevertheless, a company’s engineering expertise can enable four valves per cylinder setup when using SOHC as we can see in Yamaha Aerox 155. Since there is a significantly wider open place for air to reach the cylinder and vapours to exit when the valves are open, this configuration enables for more flow of air than two valves per cylinder.
Since the valve train’s volume is reduced in this setup, a SOHC 4 valve motor will have more rotational speed at the low end. In contrast, a DOHC setup will generate less rotational speed at first with the same number of valves due to the greater volume of the valve train, however, the upper edge performance will be higher. Another benefit of using two valves per cylinder is that it reduces the number of components, which cuts costs and complexity. The style is also superior for low and mid torque because the air circulation is quicker at these operating speeds due to the more limited flow. A SOHC layout, on the other hand, implies that the Camshaft is generally situated in the centre of the head, denying the spark plug its perfect spot.
DOHC was developed to enhance the volumetric performance of an internal combustion engine, resulting in a quite powerful motor. Camshafts can be implanted far apart thanks to this layout. This enables the inlet valves to be set at a greater angle than the exhaust valves, resulting in more effective air circulation through the motor with less blockage. In other words, a DOHC engine can breathe easier and therefore generate more power from a smaller motor displacement. In addition, in a DOHC engine, performance technologies such as Variable Valve Timing are simple to execute.
A DOHC setup makes it simple to implement a four-valve-per-cylinder setup. Almost all of the time, it enables the motor to run at a greater RPM. It also enables the valves to be positioned in an optimised configuration for enhanced efficiency. A DOHC engine with four valves per cylinder leads to a better flow of air at elevated engine velocities, leading to more high-end power. DOHC engines also enable the spark plug to be positioned directly in the centre of the combustion compartment, promoting effective combustion. The disadvantages of such a configuration include additional weight, increased prices, and the likelihood that driving two camshafts necessitates the use of more elements.
To summarise, a four-valve-per-cylinder SOHC engine found in Yamaha Aerox with a lightweight valve train volume would function best at the low end of the scale of the power band. At higher engine loads, nevertheless, a DOHC configuration with its greater valve train volume and as many valves per cylinder produces the most maximum torque and engine power.
