DOHC and SOHC: Differences explained (Which is Better?

You have likely noticed that engine specs such as SOHC and DOHC are common if you're looking to buy a car.

What do the signs actually mean? Camshaft terminology uses both terms. These two setups have some key differences.

You need to know what each engine does and why you choose it. Let’s begin

SOHC VS DOHC – What is the difference?

There are two types of engines: SOHC and DOHC. The number of camshafts is what differentiates the SOHC from DOHC. SOHC refers to a single camshaft while DOHC is made up of two camshafts.

• SOHC = Single Overhead Camshaft
• DOHC = Dual Overhead Camshafts.

DOHC engines typically have two intake valves plus one exhaust valve per cylinder. This enhances the engine's performance.

There is also some difference between these when it is coming to the performance and other aspects; let’s find out:

SOHC engine

SOHC is for one overhead cam. The SOHC engine has only one camshaft in its engine head. The SOHC engine has one intake and one exhaust valve.

DOHC engine

DOHC stands for Dual Overhead Cam. This means that there are two valves, one operating the intake and exhaust. Although the engine is equipped with one header, it has two cam rods. Contrary to the SOHC, DOHC only has one camshaft that operates the intake valves. The exhaust valves are operated by another camshaft. The camshafts can be linked by a shorter chain, but the timing belt may wrap around each gear.

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Which should I choose – DOHC or SOHC?

Now that you are aware of the differences between SOHC and DOHC engines, how do you decide which engine to choose?

These are just a few of the many differences that need to be understood.

1. Performance

Performance is what makes the difference between SOHC and DOHC engines. Due to their higher horsepower, dual camshaft engines are often fitted in more modern cars.

DOHC engines have 4 valves per engine instead of just one intake or exhaust as SOHC engines.

Older cars didn't have as much need for speed, so they could live with just one camshaft.

2. Fuel Efficiency

Because of the number of valves per cylinder – a dual camshaft engine will often have better fuel efficiency than a single camshaft engine. Fuel efficiency can be lower when there is more performance. The engine is more efficient when it's allowed to breathe.

3. Repair Costs

DOHC engines have the disadvantage of having more parts, valves and camshafts. The engine can function well with just one camshaft.

SOHC might be the engine for you if you're looking for reliability and low-performance.

4. Smoothness

The DOHC engine is also more powerful, so you'll find them much easier to control without any misfires. The DOHC engine's efficiency and ease of controlling valve timings is why this works.

If the smoothness of the engine is important to you – you should choose a DOHC engine.

SOHC & DOHC FAQ