DOHC and SOHC engines: differences, advantages and disadvantages


Before choosing a car, the future car owner is faced with a ton of information comparing thousands of characteristics. This number includes the type of engine, as well as the layout of the cylinder head, which will be discussed later. What is a DOHC and SOHC engine, what is their difference, device, advantages and disadvantages - read on.

DOHC and SOHC engines: differences, advantages and disadvantages

What is SOHC engine

DOHC and SOHC engines: differences, advantages and disadvantages

Single Over Head Camshaft (single overhead camshaft) - such motors were at their peak of popularity in the 60s and 70s of the last century. The layout is an overhead camshaft (in the cylinder head), as well as several valve locations:

  • valve adjustment by means of rocker arms, which are mounted on a separate axle, while the intake and exhaust valves are arranged in a V-shape. A similar system was widely used on American cars, the domestic UZAM-412 engine, was popular due to the excellent cylinder blowing;
  • actuation of the valves using rockers, which are acted upon by the force of the cams of the rotating shaft, while the valves are arranged in a row;
  • the presence of pushers (hydraulic lifters or thrust bearings), which are located between the valve and the camshaft cam.

Today, many car manufacturers with an 8-valve engine use the SOHC layout as a basic, correspondingly cheap version.

What is DOHC engine

DOHC and SOHC engines: differences, advantages and disadvantages

What is a DOHC engine (two overhead camshafts) - it is an improved version of SOHC, thanks to the presence of two camshafts, it turned out to increase the number of valves per cylinder (usually 4 valves), currently two types of layout are used:

  • two valves per cylinder - arrangement of valves parallel to each other, one shaft on each side;
  • four or more valves per cylinder - the valves are installed in parallel, from 4 to 2 valves can fall on one shaft of a 3-cylinder engine (VAG 1.8 20V ADR engine).

The most widespread are DOHC motors due to the ability to separately adjust the intake and exhaust phases, as well as an increase in the number of valves without overloading the cams. Now turbocharged engines exclusively have a layout with two or more camshafts, providing higher efficiency.

DOHC with two valves per cylinder

Today, such layouts are practically not used. In the 70s of the twentieth century, a two-shaft eight-valve engine was called 2OHC, and was used in sports cars such as Alfa Romeo, rally “Moskvich-412” based on SOHC type cylinder head.

DOHC with four valves per cylinder

A widespread layout that has found its way under the hood of thousands of vehicles. Thanks to two camshafts, it became possible to install 4 valves per cylinder, which means higher efficiency due to improved filling and purging of the cylinder.

How DOHC differs from SOHC and from other types of engine

DOHC and SOHC engines: differences, advantages and disadvantages

The main difference between the two types of motors is the number of camshafts and the valve actuation mechanism. In the first and second cases, the camshaft is always in the cylinder head, the valves are driven through rocker arms, rockers or hydraulic lifters. It is believed that the V-valve SOHC and the 16-valve DOHC have the same power and torque potential due to design features.

DOHC advantages and disadvantages

On the merits:

  • fuel efficiency;
  • high power compared to other layouts;
  • ample opportunities to increase power;
  • lower operating noise due to the use of hydraulic compensators.


  • more wearing parts - more expensive maintenance and repair;
  • the risk of phase out-of-sync due to loosening of the chain or timing belt;
  • sensitivity to quality and oil level.

SOHC advantages and disadvantages

On the merits:

  • cheap and easy maintenance due to simple design;
  • the ability to install turbocharged with a V-shaped valve arrangement;
  • the possibility of self-repair of motor maintenance.


  • in many respects lower efficiency, relative to DOHC;
  • high consumption relative to a 16-valve engine due to insufficient power;
  • significant reduction in engine life during tuning;
  • the need for more frequent attention to the timing system (adjusting the valves, inspecting the pushers, replacing the timing belt).



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1 comment

  1. Hello, I read your article and thanks for sharing. I have a Hyundai Elantra GLS DOHC 16V 2.0 from 01/01/2000 which, this morning after taking the road at 90km / ha, started slamming when stopped in a parking lot, the oil level is over average. I would like to have some advice

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