OHV, OHC, SOHC and DOHC are usually abbreviations that correspond to different designs of automotive engine valve train, and their main difference is in the location of the camshaft.
The term OHV (Over Head Valve) refers to an engine configuration in which the camshaft is located inside the cylinder block and the valves are actuated by pushrods, while OHC (Over Head Cam) denotes a design in which the camshaft is located inside the cylinder head and the valves are actuated directly. Cam) and DOHC (Double Overhead Cam).
There are advantages and disadvantages to the different valve train designs of each of these four types of engines, with the old-fashioned pushrod always appealing to muscle car enthusiasts, while younger enthusiasts may be more inclined to favour the DOHC.
This article will then take a closer look at all four valve train configurations and review the main differences between them.
OHV (Overhead Valve)
In an OHV Engine, the camshaft is arranged at the bottom of the cylinder and the valves are arranged at the top of the cylinder. OHV Engines are well known for their durability and longevity, and were found in early American automobiles, some trucks, and tractors.
Because of their design, OHV's are not generally used in modern Because of the OHV design, they are generally not used in modern compact cars. OHV Engines require a lot of moving parts with a lot of mass to drive them, so there is more inertia in the valves, and they would not be as efficient as a small OHV Engine, so the OHV design is better suited for larger V6 or V8 engines.
OHC (Overhead Camshaft)
The OHC design has the camshaft arranged at the top of the cylinder, the advantage of this design is that the valves are operated almost directly by the camshaft, which allows for good valve opening and closing precision at higher RPMs.
However, compared to OHV engines, OHC engines are more complex, so their timing drive systems are also longer and more complicated. The complex valve structure will make the maintenance more difficult and the maintenance cost is relatively higher.
SOHC (Single Overhead Camshaft)
SOHC is a single overhead camshaft (SOHC) system, where a camshaft is mounted on top of the cylinder and this camshaft is responsible for opening and closing the intake and exhaust valves simultaneously.
The design of SOHC is simpler, cheaper and easier to maintain than DOHC, so SOHC engines are widely used in economical family cars or motorbikes. However, due to the fact that there is only one camshaft, it is not as flexible as DOHC, and there are some limitations in timing and lift optimisation.
DOHC (Dual Overhead Camshaft)
DOHC Engine is the most complex and costly, with two camshafts at the top of each cylinder to actuate the intake and exhaust valves respectively.
This DOHC design is complex, but it also allows for higher performance, more precision, and more tuning flexibility.
Sufficiently precise valve control and better shaped combustion chambers result in better fuel combustion, which not only improves fuel economy, but also reduces harmful emissions and meets modern environmental regulations, which is why many modern car makers opt for the DOHC design.
The DOHC design has now become the mainstream design for high performance and mainstream high efficiency petrol engines because of its advantages in terms of high precision control and high efficiency, while the SOHC design continues to be widely used in economy vehicles because of its cost advantages. However, the OHV design is relatively rare in newer vehicles, and is more often used in specific areas, such as large displacement V8s, motorbikes or heavy machinery.
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