What Are the Differences Between DOHC and SOHC Engines?

Engine technology has been rapidly evolving for over a century. For example, in the early days of motor vehicles, the valves were located on the sides of the engine block. These types of engines, known as Side Valve (SV) or L-Head engines, had their valves positioned on the sides of the engine block, not at the top.

As motor technology progressed, Overhead Valve (OHV) or Pushrod engines replaced SV engines. In OHV engines, the camshaft, like SV engines, was still located inside the engine block. However, OHV engines had a significant advantage over SV engines in that the overhead valve design allowed for higher compression ratios, resulting in more powerful and efficient engines. To achieve this, OHV engines increased the number of valves in each cylinder.

Despite their advantages, OHV engines had a major drawback. The camshaft in OHV engines was still located inside the engine block, necessitating the use of pushrods to actuate the overhead valves. This limitation made it nearly impossible to use more than two valves per cylinder in OHV engines.

To address these issues, Overhead Camshaft (OHC) engines were developed. In OHC engines, the camshaft, also known as the camshaft, is located in the cylinder head, above the valves. The camshaft's motion is synchronized with the engine's rotation using a timing belt or chain. OHC engines allowed for greater flexibility in valve design and placement.

SOHC (Single Overhead Camshaft) engines were the first type of OHC engines. These engines had a single camshaft in the cylinder head, which controlled both the intake and exhaust valves for each cylinder. While this design was an improvement over OHV engines, it still limited the number of valves per cylinder to two.

The need for more valves per cylinder led to the development of DOHC (Double Overhead Camshaft) engines. In DOHC engines, there are two camshafts in the cylinder head—one for the intake valves and one for the exhaust valves. This design allows for more precise control of valve timing and the use of multiple valves per cylinder, typically four (two intake and two exhaust). DOHC engines are known for their high performance and efficiency.

In summary, the main differences between DOHC and SOHC engines are the number of camshafts and the control of valves. SOHC engines have a single camshaft that controls both intake and exhaust valves for each cylinder, while DOHC engines have two camshafts—one for intake valves and one for exhaust valves—allowing for more valves per cylinder and finer control of valve timing.