What is the difference between SOHC and DOHC engines?
3 Answers
SOHC engine refers to its intake system using a single overhead camshaft, which means one intake valve and one exhaust valve; DOHC engine refers to its intake system using double overhead camshafts, generally with multiple valves per cylinder, commonly 4 valves. DOHC has two overhead camshafts placed on the cylinder block, the first one drives the intake valves, and the second drives the exhaust valves; SOHC, a single overhead camshaft in the cylinder head uses one camshaft to directly drive the intake and exhaust valves, featuring a simple structure and is suitable for high-speed engines. The single camshaft has a simpler mechanical structure, fewer issues, and greater low-speed torque. The opening times of the intake and exhaust valves in a single camshaft are fixed, but its mechanical simplicity, ease of maintenance, and fuel efficiency are all advantages of SOHC. The double camshaft can adjust the valve overlap angle, thus delivering greater horsepower, but it lacks low-speed torque and, due to its more complex mechanical structure, has higher manufacturing costs and maintenance expenses. The double camshaft technology originates from racing, primarily to control the timing difference between the intake and exhaust valves. Neither is inherently better; single and double camshafts are just structurally different.
I've been driving for over a decade, and the difference between SOHC and DOHC engines mainly lies in daily usage. SOHC stands for Single Overhead Camshaft, meaning there's only one shaft controlling valve operation, with simple structure and affordable maintenance. My first old car had an SOHC engine - it ran smoothly with good fuel economy and gentle acceleration, perfect for city commuting. But it responds slowly at high RPMs, lacks power during gear shifts, and struggles with highway overtaking. DOHC (Dual Overhead Camshaft) features two independent shafts separately managing intake and exhaust valves for more precise control. My current DOHC car accelerates faster, responds more sharply, and maintains better stability at high speeds, though it's more expensive and requires extra attention to the lubrication system during routine maintenance due to its complexity. If you frequently take long trips or enjoy responsive acceleration, DOHC is more suitable. Otherwise, SOHC suffices and saves money. Choosing the right type based on road conditions prevents throttle lag during acceleration, which impacts driving pleasure and safety in the long run - these details are crucial when selecting used cars.
SOHC engines feature a simple design with a single camshaft controlling all valves, offering stable operation, low cost, and are commonly found in family cars. I've modified a few; they're easy to maintain with affordable parts—even changing spark plugs is a DIY job. However, their main limitation is less precise valve control, which can lead to valve float at high RPMs, restricting power output. DOHC systems, with dual camshafts separately managing intake and exhaust valves, handle high RPMs better, allowing the engine to 'breathe' more smoothly—ideal for performance cars. I drove a modified DOHC once; it showed noticeable acceleration on climbs and highways, with quieter operation. Yet, its complex structure adds weight and fuel consumption, requiring professional tools for tuning. For drivers seeking thrills or frequent mountain roads, DOHC is recommended, while SOHC suits budget-conscious daily use. Also, material differences affect longevity—don’t overlook routine valve clearance adjustments to prevent long-term wear.
