What is the difference between single overhead camshaft and double overhead camshaft?
2 Answers
A single overhead camshaft (SOHC) is arranged with one camshaft in a cylinder head, while a double overhead camshaft (DOHC) has two camshafts in a cylinder head. Both SOHC and DOHC designs allow the engine to operate at higher speeds. The main differences between them are as follows: 1. Driving method: The SOHC drives the intake and exhaust valves through rocker arms to achieve opening and closing, while the DOHC uses one camshaft to control the intake valves and another to control the exhaust valves. 2. Usage scenarios: Engines with SOHC are almost obsolete, typically found in older engines with outdated technology. DOHC is essential for multi-valve engines. If each cylinder has three to five valves, DOHC must be used. Most modern engines adopt DOHC design, with each cylinder having four valves—two intake and two exhaust. This design allows for more efficient air intake, more thorough exhaust, improved engine efficiency, and reduced fuel consumption. DOHC can also be paired with variable valve timing and variable valve lift systems for intake and exhaust, further enhancing engine efficiency and fuel economy. Therefore, most current engines use DOHC design.
I've been repairing cars for over a decade. The single overhead camshaft (SOHC) uses just one camshaft to control both intake and exhaust valves, making it structurally simple, easy to maintain, and cost-effective, though with moderate performance. The double overhead camshaft (DOHC), on the other hand, employs two independent camshafts separately managing intake and exhaust, allowing the engine to breathe more smoothly, rev higher, and deliver stronger output. Don't underestimate this difference—during high-speed or aggressive driving, DOHC responds much faster, which is why modified race cars often prefer it, though it comes with more parts and higher maintenance costs. For daily driving, SOHC is sturdy and durable, making it ideal for regular family cars. It really depends on the vehicle match—some older engines with well-designed SOHC can still hold their own.
