OHC vs. SOHC vs. DOHC: What Is The Difference?


Know More About Engine Terminology – OHC, SOHC, DOHC:

Conventional Valve Operating Mechanism:

Before OHC: The engine cylinder block housed the camshaft next to its crankshaft in older conventional engines. The cylinder head at the top housed the engine’s valves. The camshaft operated a range of parts such as the rocker arms, push-rods, and tappets that, in turn, operated the valves.

The conventional valve operating mechanism
The conventional valve operating mechanism

This design applies to slower-speed engines. It involves many moving parts and results in sluggish engine response. However, the passenger cars needed refined high-speed engines. So, the engineers replaced this technology with a more sophisticated ‘Over Head Camshaft’ design mechanism or the OHC.

What is OHC?

The term OHC stands for Over Head Camshaft. This valve arrangement configuration places the camshaft in the cylinder head above the pistons and combustion chamber. Such a camshaft operates the valves or lifters directly. This design is opposed to the conventional overhead valves, operated by ‘rocker arms’ & push-rods.

OHC Enigne
OHC Engine

What is SOHC:

Firstly, the term SOHC stands for Single Over Head Camshaft. This design uses only one camshaft placed in the cylinder head. Typically an in-line engine with a single has cylinder head with one camshaft at the top of the cylinder head. Thus, it is opposed to the bottom position in the cylinder block, which the conventional design used.

How SOHC Works?

Usually, this lone camshaft operates both the inlet and exhaust valves. Using the OHC type of design eliminates the need for some parts such as rocker arms, push-rods, and rocker-arm tubes. Thus, it results in a more straightforward design and smoother and quieter engine operation. It also helps to reduce weight and maintenance costs.

SOHC - 'Single Over Head Camshaft' mechanism
SOHC – ‘Single Over Head Camshaft’ mechanism

An engine with multiple cylinder heads, such as a ‘V-engine’ or a flat (horizontally-opposed) engine, uses two camshafts, one for each cylinder head. However, this lone camshaft itself operates both the Inlet & Exhaust valves.

Example of cars with SOHC engine:

  1. Honda’s 1.5L i-VTEC SOHC engine
  2. Tata Motor’s 475 IDI SOHC engine
  3. Maruti Suzuki’s 800 cc SOHC engine

What is DOHC?

Secondly, DOHC stands for Double Over Head Camshaft. This newer-generation design uses two separate camshafts instead of the common camshaft. One of them operates the inlet valves exclusively, while the other handles the engine’s exhaust valves. This design is implemented in modern-day motors as it provides better control on the opening & closing of valves. Thus, it results in improved performance of the engine.

DOHC - 'Double Over Head Camshaft' mechanism diagram
DOHC – ‘Double Over Head Camshaft’ mechanism diagram

How DOHC Works?

DOHC design allows a wider angle between intake and exhaust valves than SOHC design. Thus, it helps improve breathing and scavenging (removing exhaust gases) from the engine. Additionally, this design does not restrict the airflow. Instead, it allows smooth passing of air at higher engine speeds, which results in better performance and faster engine response.

Examples of cars with DOHC Engine:

  1. DC Avanti’s 2.0-liter engine
  2. Honda’s i-DTEC DOHC engine
  3. Ford’s EcoBoost DOHC engines
  4. Tata Motor’s DiCOR DOHC engine

Watch Ford’s EcoBoost DOHC engine in action here:

Read More: What is 4-valve Technology in engines?>>

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