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What’s The Difference Between “DOHC Vs. SOHC”?

What's The Difference Between "DOHC Vs. SOHC"?

Are you looking for a new vehicle? If so, you have already found that there is often a reference to a SOHC or DOHC engine.

But what do these signs mean? 🤔

Both terms do use in regards to the camshaft. There are some significant differences between these two types of setups.

Before you decide which to choose, DOHC vs. SOHC, you need to understand what they mean and how they operate.

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What is a SOHC Engine?

SOHC stands for a single overhead cam. This type of engine comes with only one camshaft located in the engine head.

With the SOHC engine, you do most often have one intake valve and one exhaust valve.

What's The Difference Between "DOHC Vs. SOHC"?

SOHC Engine Advantages

The SOHC design offers several advantages over the cam-in-block design:

Valves can be positioned for the best combustion chamber design. Multiple valves can be employed; as many as five per combustion chamber are possible.

Dual spark plugs can be utilized as well. These improvements can improve fuel-air flow and combustion capabilities offering increased power and better fuel economy.

Passageways through the engine block and cylinder head for pushrods do not require. Both areas can thus employ additional (or more oversized) coolant passages improving cooling efficiency.

Upgraded cooling, especially in the cylinder head areas, can enable higher compression ratios. This benefits both power output and fuel economy.

– The mechanism operated by the camshaft to open the valves can be both simpler and lighter. This reduces the opportunity for valve float making much higher engine speeds possible.

Higher RPMs, in general, enhance power output.

Access to all components of the valve system, especially the camshaft, is simpler. Repairs to this critical area of the engine would then be less costly.


SOHC Disadvantages

There are some disadvantages to the SOHC engines when compared to the cam-in-block designs as well as to the DOHC designs:

– Engine complexity is increased. This adds to design and manufacturing costs. There may also be an overall increase in engine weight compared to cam-in-block designs.

Camshaft drives using a chain or a belt can introduce reliability and maintenance considerations not common to cam-in-block engines.

– The engine can become taller and require increased hood height for clearance. Due to the engine size increase, weight may be increase also.

– Variable valve timing is primarily restricted to timing changes for both intake and exhaust valves simultaneously. This is the same timing problem that exists for cam-in-block engines.

What is a DOHC Engine?

DOHC is a synonym for dual overhead cam, and this means you have two cams operating the exhaust and intake valves. 

The engine has one header but with two cam rods. 

Unlike the SOHC, the DOHC has one camshaft operating the intake valves and another camshaft operating the exhaust valves. 

What's The Difference Between "DOHC Vs. SOHC"?

The camshafts do often tied together by a short chain but sometimes, the timing belt wrap around both gears.

The difference between SOHC vs. DOHC engines is the number of camshafts in the car engine. 

SOHC means that there is one single camshaft, and DOHC means that there are dual camshafts. 

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

The engine is most often runs 2 intake valves and 2 exhaust valves per cylinder with DOHC engines, instead of 1 intake and 1 exhaust valve on the SOHC engine. 

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The Function of Timing Belts

DOHC Advantages

DOHC engines share the same advantages as the SOHC designs. 

These include:

Valves can be positioned for the best combustion chamber configuration. Power and fuel economy can benefit by optimizing the valve arrangement.

Engine block and cylinder head cooling efficiency do enhance with DOHC designs. Increased compression ratios offer increased power and fuel efficiency.

– DOHC designs offer the most direct operation of the valves. Peak engine RPMs of 8,500 or higher are possible for street automobiles.

Racing vehicles can attain even higher engine speeds with advanced DOHC systems.

– Maintenance accessibility to the camshafts and lifters is easier. This can help reduce overall maintenance and repair costs.

– DOHC engines make possible the best VVT benefits.

Variable valve timing can operate independently for each camshaft providing optimum valve timing for both the intake and exhaust valves.

DOHC Disadvantages

As with SOHC engines, DOHC designs share the same fundamental disadvantages.

– Engine complexity and weight are increased compared to cam-in-block designs. Design and manufacturing costs are higher as well.

Compared to SOHC designs, DOHC engines have a more complex chain or belt drive system. This decreases overall reliability and adds to maintenance expense.

– As with SOHC designs, DOHC engine height is increased, and overall weight also tends to be higher. This increases the performance.

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

DOHC or SOHC? Which should I choose?

So now, when you know the difference between a SOHC or DOHC engine, which one should you choose, and what are the pros and cons between these engines?

There are actually a lot of differences between these that you need to know about.

1. Performance

The main difference between the DOHC and SOHC engines is the performance. 

Dual camshafts do often produce more horsepower, and it is therefore often equipped in newer cars.

This is because DOHC engines often use 4 valves per cylinder instead of one intake and one exhaust like SOHC engines.

Older cars had not the same need for performance, and therefore, they were fine with a single 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. 

More performance can often lead to lower fuel efficiency. 

This is because of the much more efficient engine when you let it breathe properly.

3. Repair Costs

The downside of the DOHC engine is that you have many more valves, camshafts, and parts that can break down. 

A single camshaft requires far fewer parts for the engine to function correctly.

If you are looking for a reliable engine without too much performance, SOHC is probably the right choice for you!

4. Smoothness

Because the DOHC engine also gives a more excellent performance, you will often find these much smoother without misfires. 

This is because of the efficiency and easiness to control valve timings.

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

Click To Read:

Valve Mechanism Construction


Which is better, SOHC or DOHC?

That depends on what you are looking for. DOHC is better for performance because you will get more horsepower with it. SOHC is better for reliability. 

A SOHC engine contains much lesser parts, which will make it more reliable.

What is the advantage of DOHC?

DOHC engine is much more efficient, and you will get more power output from the engine. 

A DOHC engine will therefore also have better fuel consumption because of the efficiency.

Is SOHC a good engine?

The SOHC engine is a good engine type, but it depends on what you are looking for.  If you are looking for a reliable engine, the SOHC is a good engine for you. 

If you are looking for performance and good fuel consumption, DOHC is a better choice.

How do I know if I have DOHC or SOHC?

The easiest way is to check the specifications of your car repair manual or something similar. You can often also check the width of the engine cylinder. 

If it is wide, there are probably two camshafts, and if it is too narrow to contain two camshafts – you have a SOHC engine.


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