What Are The Differences Between DOHC & SOHC?

Engine type is often a consideration and this may be based on the fuel it uses, the cylinder style, horsepower, torque and a host of other things. In this article we will be looking at the choice between SOHC and DOHC.

Those with a particular interest in all things automotive may already know what these initials mean but for those who do not we will explain that today. We will also look at how these two differ and which might be the best option for your next car purchase.

What Is a Camshaft?

We will start out addressing the C in SOHC & DOHC, this stands for Camshaft. Essentially the camshaft is the part of your engine that is responsible for opening and closing the various valves. It is not only the intake valves but also the exhaust and it must do so in a synchronized and precise manner.

Small bulges on the camshaft are what activate the opening of the specific valves. This will ensure that the engine receives the air it requires to operate as efficiently as possible.

Generally made of a cast iron alloy or hardened steel it is rotated either by a timing belt or chain. It connects to this belt by sprockets and also to the car's camshaft. This allows them to work in unison for better performance.

What Is the Difference Between a DOHC and SOHC Engine?

The difference between these two engines is one of simple quantity with regards to the camshafts. The Single Overhead Camshaft (SOHC) has one while the Dual Overhead Camshaft (DOHC) has two. These camshafts are located in the cylinder head and most modern vehicles fall into one of these two categories.

Obviously there are benefits and drawbacks to both options so in the following sections we will take a closer look at both types of camshaft setups.

Single Overhead Camshaft Setup

In a single overhead camshaft motor you unsurprisingly get just the one camshaft in the cylinder head. Depending on the type of motor this camshaft will either use cam followers or rocker arms to open the intake and exhaust valves.

Most frequently these types of engines will have two valves, one each for the intake and exhaust although some might have three with two of them being for exhaust. These valves are for each cylinder. Certain engines may have four valves in each cylinder, for example the 3.5-liter Honda engine.

Regardless of whether the engine configuration is flat or in a V there will be two cylinder heads and subsequently two camshafts total.

SOHC Pros SOHC Cons
Simple Design Restricted Airflow
Fewer Parts Less Horsepower
Simple to Manufacture Efficiency Suffers
Less Expensive
Solid Mid to Low Range Torque

Dual Overhead Camshaft Setup

As mentioned and unsurprisingly the DOHC type engine will have two camshafts on each cylinder head. The first will run the intake valves with the other taking care of the exhaust valves. This allows for four or more valves per cylinder but generally at least two each for intake and exhaust.

DOHC motors usually use either lifter buckets or cam followers to activate the valves. Depending on how many cylinder heads the engine has each one will have two camshafts.

DOHC Pros DOHC Cons
Better Airflow More Complicated
Supports Better Horsepower Harder to Make Repairs
Increased High-end Torque Takes More Time to Manufacture
Boosts Rev Limits Costs More
Allows for Efficient Tech Upgrades

Which Is Best, DOHC or SOHC?

So the big question is which configuration is the best and which should you choose? As with all things automotive there will always be two sides of the argument so ultimately the choice belongs to the buyer. We will however do a little more comparison to perhaps help you make an informed decision.

Which Is Most Fuel Efficient?

When it comes to fuel efficiency if you had the same model car one with DOHC and the other with SOHC you would have an argument for better fuel economy on both. The SOHC for example would be a lighter vehicle than the DOHC so it should have better fuel economy. The DOHC however would have better airflow and be more efficient based on that but less so because of weight.

The truth is it is a case by case basis and you would best look at the option that can claim the best fuel economy if that is something you prize. This could fall into either overhead camshaft category.

Cost of Maintenance

Generally speaking we have a clear winner when it comes to lower maintenance costs and that is the SOHC setup. There are fewer parts to go wrong and the setup is more simple. A DOHC engine has a complex belt or chain drive which will add to potential maintenance expenses.

Performance

Having taken the lead the SOHC must look on as DOHC levels things back up again. When it comes to performance the DOHC setup is just better. The additional valves create better performance and the added airflow really makes a difference.

The timing of the DOHC system is also more precise and controlled than that of an SOHC setup. Essentially Dual camshafts just make for a stronger, better performing engine.

Price

Another easy win for the SOHC setup without question is that it is cheaper than a DOHC version. The SOHC is simpler to make and costs less money and is cheaper to maintain. When it comes to DOHC it’s more complicated, includes more parts and simply costs more to put together.

Responsiveness

The DOHC is going to close the gap yet again in terms of responsiveness and general smoothness of the system. The additional valves in the DOHC setup make things run more smoothly and get a better response than just the single camshaft.

Final Verdict

This is all going to boil down to what you want from your vehicle the most. If simplicity of maintenance and lower costs overall are important to you then you might choose a Single Overhead Camshaft setup. However if you want better performance and improved quality and are willing to pay the price Dual Overhead Cams may be the way to go.

A cheaper car that has fewer elements to break down as compared to a more expensive better performing car that has more potential issues that might arise. It is a hard call unless you are firm in your preferences. Hopefully we have been helpful in our article today and you understand the differences between the two systems now.

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