Single Overhead Camshaft VS Dual Overhead Camshaft

SOHC VS DOHC
These represent the valve configuration inside an engine cylinder head to control the action of the valves.

Though these configurations are renowned for their superior performance, both have some significant differences.

SOHC stands for Single Overhead Camshaft
This type of valve configuration utilizes only a single camshaft, for operating both intake and exhaust valves.

DOHC or Dual Overhead Cam on the other hand,
Utilizes two independent camshafts for the operation of the intake and exhaust valves. Let’s have a look at the single overhead camshaft configuration.

An Single Overhead Camshaft engine head is packed with,

  • Intake valves
  • exhaust valves
  • Rocker arms
  • Rocker arm shafts
  • Single camshaft

The camshaft is designed in such a manner that the cam lobes could push the rocker arms at corresponding timings to open the valves. The return springs ensure that the valves lift back afterwards, and keeps tension back on the lobes.

SOHC design typically allows a 2 or 3 valves per cylinder configuration,

  • 2Valves Per Engine Cylinder
  • One Intake Valve
  • One Exhaust Valve

3Valves Per Engine Cylinder

  • Two Intake Valve
  • One Exhaust Valve

However, current industrial competencies allow production of four valves- per cylinder configuration using SOHC.

4Valves Per Engine Cylinder

  • Two Intake Valve
  • Two Exhaust Valve

Due to the reduced count of parts, the design complexity and manufacturing cost is comparatively low for SOHC engines.
Since the mass of the valve train is lesser in such a configuration, single overhead camshaft engines tend to produce more torque towards low to mid RPM and provide improved fuel efficiency.

The DOHC was later introduced with improved volumetric efficiency for an internal combustion engine. In this configuration, the head is packed with

  • Intake valves
  • exhaust valves
  • Cam followers
  • two independent camshafts

DOHC uses two separate camshafts per bank of the cylinder head. This allows all the cam lobes to directly operate the valves rather than using rocker arms as in SOHC engines.
Here also, the return spring ensures that the valves lift back and keeps the tension on the camshaft lobes.
DOHC usually implements a

Four valve per cylinder configuration

  • Two valves for intake
  • Two for exhaust

This configuration has a better valve lift resulting in improved airflow through the combustion chamber. With less airflow restriction, the DOHC engine is even capable of generating more horsepower out of smaller displacement.
Though this configuration can provide better top end power, the design complexity and increased components results in more weight and a higher cost of production. When it comes to choosing between SOHC and DOHC engines, both have it’s own pros and cons. Let’s look at some points briefing the presentation

Single Overhead Camshaft

  1. Uses a single shaft to drive all valves
  2. Fewer components makes less in weight
  3. Better torque at low to mid range RPM
  4. Cost effective at manufacturing
  5. Fuel efficient due to fewer parts consuming energy
  6. Camshaft being at the center denies the ideal location for spark plugs

Dual Overhead Camshaft

  1. Uses two independent shafts to operate the valves
  2. Complex design and increased production cost
  3. Improved volumetric efficiency with better airflow
  4. Makes the engine capable of revving up to higher RPM
  5. Better top end torque and increased horsepower
  6. Capable of implementing efficiency enhancing technologies like VVT

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