Engine technology is evolving and improving every passing day. There are several existing options that different automakers and engine designers use when coming up with an engine.
The two most common types of camshaft engines in the market today are SOHC and DOHC. All the camshaft engine types have three elementary components in their head that trigger the exhaust and intake.
They include valves, rocker arms, and camshafts. There is a lot of argument on which engine design is better between the SOHC vs. DOHC.
Below we shall discuss the differences between SOHC vs. DOHC engines. We will also state their downsides and upsides. The information will help you to select the engine type that fits your needs.
What does camshaft mean?
A camshaft is a vital piece of an internal combustion engine as it opens and closes the intake and exhaust valves in the engine. When opened, an air-fuel mixture enters the cylinder while the exhaust gas leaves the engine.
A crankshaft drives a camshaft. A camshaft is made up of a series of cams or lobes that push against valves and open and close the valves according to setting timings.
Functions of a Camshaft
Camshafts are oval shaped lobes in the head of each cylinder; they are primarily responsible for regulating the timing and operation of the intake and exhaust valves i.e. opening and closing the valve at a specific interval.
Performance: The shape of the valve lobe greatly influences the power output and torque delivery. In high performance engines, the cam lobes are designed to keep the valve open for longer, in order for more air-fuel mixture to flow in the engine for enhanced performance.
Valve Timing: The efficient opening and closing of intake and exhaust valve in sync with the position of the piston is controlled by the camshaft. It ensures ideal engine timing for optimum efficiency and power delivery.
When a single camshaft governs both intake and exhaust valves, the setup is commonly known as SOHC.
On the other hand, in a DOHC setup, there are two dedicated camshafts, one to push the inlet valves and the other to push the ones which let the gases escape from the cylinder after combustion.
In both instances, the camshaft is positioned above the valves for more accurate actuation. There is also another setup called OHV (Over Head Valve) which is traditional and less efficient than the other two, and is rarely adopted these days.
In an OHV design, the camshaft is installed inside the engine block and valves are operated by lifters, pushrods and rocker arms. For this very reason, an OHV engine is also known as a “pushrod” engine.
The main disadvantage of an OHV design is that it’s difficult to precisely control the valve timing at high rpm because of the higher inertia caused by a larger amount of valve train components.
This makes an OHV design better suited for engines with large volume which offer higher torque at lower RPMs. With the basics out of the way, let us now understand what are the advantages and disadvantages of employing a SOHC or a DOHC setup.
What is an SOHC Engine?
A single overhead camshaft (SOHC) engine has just one camshaft located in the cylinder head. Depending on the engine design, the camshaft may operate either rocker arms or cam followers to open the individual intake and exhaust valves.
SOHC engines typically have either two valves (one exhaust and one intake) or three valves (one intake and two exhaust) per cylinder. But there are some SOHC engines, such as Honda’s 3.5L, that use four valves per cylinder.
It’s also important to note that SOHC engines with a ‘V’ or flat configuration have two cylinder heads. Each of those cylinder heads has a camshaft inside.
What is a DOHC Engine?
A dual (or double) overhead (DOHC) engine has two camshafts per cylinder head. One camshaft operates the intake valves while the other operates the exhaust valves. The design easily allows for four valves (two intake and two exhaust) per cylinder.
In most DOHC engines, the camshafts act on cam followers or lifter “buckets” to open the individual intake and exhaust valves. DOHC engines with two cylinder heads have four camshafts (two per cylinder head).
Difference Between SOHC and DOHC Engines
SOHC and DOHC differ in many ways. Physically, the SOHC has a single camshaft while a DOHC has twin camshafts over the head of the engine.
Apart from this physical difference, their performance is also not the same. These are the differences between the two engines:
DOHC Engine
- The Double Overhead Cam has two camshafts. One is used explicitly for the inlet, and the other only regulates the outlet. The engine has two pairs of inlet and exhaust valves.
- DOHC has twin camshafts making it much more flexible in tuning and optimum valve timing. This enhances the maximum attained horsepower.
- DOHC consumes more power due to the enhanced control of the valves. When the power consumption is high, fuel consumption is also high. However, some factors like the gear transmission, the experience of the driver, the design of the engine, and the age of the car also determine the fuel efficiencies.
- Spark plugs in the DOHC engines are located at the center of the combustion chamber since it operates both in the exhaust and intake. This results in fuel efficiency due to enhanced combustion. The spark plugs are located strategically, which leads to efficiency and increased performance.
- DOHC has more top-end power. With the same number of valves, DOHC has more top-end power at higher speeds. Its performance is also enhanced since you can attach more valves in individual cylinders.
- DOHC has a different setup for both outgoing and incoming gasses. It has twin valves making it complicated and thus more expensive to manufacture. It is also more costly when it comes to repair and maintenance. The technological innovations in valve timing favor the DOHC engines more.
- DOHC has multiple valves taking control of the intake and exhaust. This makes the ride smooth and noise-free.
SOHC Engine
- Single Overhead Cam engine has one camshaft that regulates both the outlet and the inlet of gasses. This engine has one pair of exhaust valves.
- SOHC engines have a single camshaft which leads to less control of valve timing. The internal combustion engine operates when the air and fuel mixture ignites. The process of ignition needs the timing of injecting fuel and removing exhaust gases to be accurate. The angle of the camshaft influences the timing of the Exhaust and intake of the gasses. The horsepower will be more when you have better timing.
- SOHC is more fuel-efficient since its power consumption is low.
- The spark plugs are not located at the center of the cylinder. They are not strategically located, thus hindering the performance of the SOHC engine.
- SOHC has a better low-end torque. If a SOHC engine has 16 valves, it produces better torque, at low speed. The performance is however much less, especially at high speed.
- It is more affordable since it has a single cylindrical rod that regulates the exit and intake gasses. The design is less complicated; thus, the manufacturing cost is low. The maintenance and repair costs are also low.
- Only a single set of valves controls the inlet and outlet in SOHC; thus, the engines produce some noise.
Pros And Cons Of SOHC And DOHC Engine
SOHC engine
SOHC stands for Single Overhead Cam (Only one cam rod operating the intake and exhaust valves).
That means there is only one camshaft in the head. Inline engines will have one camshaft. The flat engine and V-engine will have two camshafts, one per cylinder bank.
Pros
- At low speeds, SOHC engines will produce more torque than DOHC engines of the same capacity.
- The simple structure (just has one cylindrical rod) due to the reduced count of parts, the design complexity and manufacturing cost are comparatively low for SOHC engines so its price will be more affordable.
- Because this engine is quite common on the auto market, it is easy to find a repair place when it breaks down, and the cost of repair and replacement is also much lower.
Cons
- SOHC only allows using 2 valves per cylinder, so the same capacity will give a lower capacity compared to DOHC engines.
- SOHC engines because the camshaft must be located in the middle of the combustion chamber to drive both the intake/exhaust valves, so the spark plugs are not positioned at the center of the car cylinder. This design is not a logical arrangement that will prevent partly the performance of the SOHC engine.
DOHC engine
DOHC stands for Dual Overhead Cam or Double Overhead Cam (there are two cams located overhead operating various intake and exhaust valves). That means each header has two camshafts.
Hence, an inline engine will contain 2 camshafts as it has only one header. The flat engine and V-engine will contain 4 camshafts as they have two headers.
The DOHC engines usually come in 4 valves. One camshaft for the intake valves and the other for the exhaust valves.
Pros
- The DOHC was later introduced to improve volumetric efficiency for an internal combustion engine.
- DOHC usually implements a four-valve per cylinder configuration (two valves for intake and others for exhaust), so the same capacity level will give a much larger capacity than the SOHC engine. This configuration has a better valve lift resulting in improved airflow through the combustion chamber. It can create more horsepower out of the smaller displacement.
- At high speeds, the maximum torque and power of DOHC are higher than SOHC, making the machine stronger.
- The location of the spark plug in the middle of the top of the combustion chamber helps the DOHC engine to have better fuel combustion efficiency.
- DOHC engines also possess the advantage of being able to apply variable valve technology, adjusting the camshaft to optimize the operating mode.
Cons
- High cost because the engine structure is complicated with many details and requires higher technology. When there is damage to repair, it requires meticulousness and skilled mechanics. And of course, the replacement and repair cost will be more expensive than the SOHC engines.
- The bulky structure increases the weight of the vehicle, which partly affects the ability to operate, or forces the manufacturer to minimize some details to balance.
Which is Better: SOHC or DOHC Engine?
When comparing the two, one should consider the driver’s needs. While both have their respective advantages, their suitability will depend on how they are used daily and whether performance and fuel-economy standards are met.
For Daily Use
- Stable: SOHC engines deliver smoother and quieter rides, ideal for urban commutes and day-to-day use.
- Cheaper to Maintain: Being less complicated and with fewer components, SOHC engines are less expensive.
- Fuel Efficiency: SOHC engines, planned and designed with a fuel efficiency strategy as a priority, will tend to be more economical and, hence, consume less fuel.
For Performance Enthusiasts
- More Performance: DOHC engines incorporate more valves, improving the air-fuel mixture and exhaust intake.
- Improved Acceleration: With their degree of adjustment and enhanced power delivery, DOHC engines are the choice for anyone who wishes to accelerate.
- Advanced Technology: High-tech DOHC engines regularly come with features such as variable valve timing to capture the interest of motorsport enthusiasts.
FAQs.
Q: What Is The Advantage Of DOHC?
The major advantage of DOHC engines is that they easily integrate four valves for every single cylinder, which include two exhaust valves and two intake valves. The four valves in the cylinder allow a smoother flow of gases and fuel both out and in the cylinder.
The four-stroke cycle, therefore, increases the performance mainly at high speeds. Secondly, the diesel injector or the spark plug is located at the center of the cylinder, which increases efficiency in the burning of the fuel and air mixture.
Q: Why Does DOHC Make More Power?
DOHC engines have a high performance, make more power, and can run at higher speeds. The engines have less inertia which allows extreme cam profiles at higher speeds.
Power is calculated by multiplying the engine speed and torque. It means that you will make more power when the crank spins faster.
This engine also has separate exhaust and intake valves, which enables the cam phasing to be continuously altered when in use. This allows a single engine to be tuned for both high and low rpm power.
The engine makes more power when more air gets into the cylinder, and it will waste less power if it is able to pump the exhaust out of the cylinder easily.
The four valves in the DOHC engine allow the engine to inflate sufficient air to run and produce useful power at high speeds.
Q: What Is The Best DOHC or SOHC?
The engine type you choose should be based on your needs. SOHC and DOHC engines are different, and they both have their upsides and downsides. The Single Overhead Camshaft means that you have a single camshaft working both for the exhaust and intake valves.
SOHC engines are cheaper to manufacture, maintain, and repair. Their fuel efficiency and performance, however, cannot be compared with that of DOHC engines.
DOHC engines have two camshafts one which controls the intake valves while the other is responsible for the exhaust valves.
SOHC engines are fuel-efficient, but DOHC can reflect more fuel efficiency depending on the design of the engine and the skills of the driver. The Dual Overhead Camshaft also has better valve timing compared to its counterpart.
The spark plug in the DOHC engine is optimally placed thus improving the combustion efficiency.
We can simplify this by saying that DOHC has a better high-end power while SOHC has better low-end power. DOHC is more expensive, but they are worth the investment.
Q: How Many Camshafts Does a DOHC v8 Have?
The DOHC v8 has four camshafts. Dual Over Head Camshaft means that each cylinder has two camshafts at the top of the engine head. Engines that have more than a single cylinder bank, like the V8 and V6, have two camshafts per cylinder head.
Q: Is Twin Cam And DOHC The Same?
A twin-cam is an engine with two camshafts that operate both the exhaust and intake valves.
One camshaft operates the exhaust valves while the other controls the intake valves. It is, therefore, the same as the Double Overhead Camshaft. They are more efficient and have higher power than SOHC engines.
Final Words
SOHC vs. DOHC engines is quite different. The type of engine you choose should be based on your needs. The SOHC has a single camshaft while the DOHC has double camshafts on top of each cylinder head. It has better fuel efficiencies at high speed compared to SOHC.
The older vehicles were manufactured with SOHC engines while the modern cars are made with DOHC engines.
The efficiency in valve timing in the DOHC has made the engines to be quiet and cooler when on the move. The extra valves make the vehicles heavier but their performance levels are quite high.
At low torque, the DOHC and SOHC produce the same power, but DOHC makes more power as you increase the rpm. You can perform some engine swaps if you want to upgrade from SOHC to DOHC.