The valves in a car’s engine let the air/fuel mixture into the engine and the exhaust out of it. This is a necessary component of internal combustion. One of the most important parts of a valve is the camshaft. This is composed of a cylindrical rod running the length of the cylindrical bank with a number of lobes, called cams. The cams push against the valves to force them open as the camshaft rotates. During this process the cams open and close the intake and exhaust valves in time with the stroke of the piston.
The camshaft can impact the performance of an engine at different speeds. There are two basic configurations of camshafts: Single Overhead Camshaft or SOHC, Dual Overhead Camshaft or DOHC (also called Double Overhead Camshaft). These simply refer to the number of camshafts on the cylinder head.
In a Single Overhead Camshaft configuration, there is only one cam per head. For an inline-4 or an inline-6, there is only one cam. For a V-6 or a V-8 engine, it will have two cams – one for each head.
A Dual Overhead Camshaft configuration has two cams per head – one for the intake valve and another for the exhaust. So a double overhead cam inline engine would have two cams, while a V engine would have four. It is important to note that having two cams, in and of itself, does not necessarily mean more power for your car. The total size of the valves matter more. Having two does allow better control and less complexity in multi-valve engines.
For both the single and double overhead cam engines, the cams are driven by a crankshaft through the timing belt. In a two-stroke engine the camshaft opens the valve once for each rotation of the crankshaft. In these engine types, the camshaft and the crankshaft have to be in synch. In a four-stroke engine, on the other hand, the valves are opened only half as often as in a two-stroke engine. It takes two full rotations of the crankshaft for the camshaft to make a full rotation. Controlling the timing of the camshaft can produce better torque – advancing it produces better low-end torque and retarding it produces better high-end torque.
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