Are you in the market for a car and you frequently stumble upon the names SOHC and DOHC? You probably wonder what do these letters mean and which is the winner in the SOHC vs DOHC duel? We are going to cover that and more in this article. So, follow us till the end when we will give our recommendations on the route you should go.
Getting a new car can be a difficult task and often confusing one, since there is a lot of letters, numbers, and other information that you need to gather. Then you need to cramp all that data in your mind and then look for the best deal out there.
That’s why you need to learn terms like these two. You need to learn what is SOHC and what is DOHC. Because there could be a lot of difference between the two and how your car will drive on the street and also how your engine is going to perform. Not to mention the fuel efficiency and other important things that will make a huge difference for you as a car owner. That’s why we are going to help you out with that and will make your life easier.
In this article, we are going to learn what do these terms mean. We will elaborate in detail and we are going to learn all the important bits. Then we will compare SOHC vs DOHC and we will share our opinion on which one you should get. Then we will discuss the things from a repair perspective and see which of them is easier to fix. So, let’s get into it.
What Is SOHC?
SOHC or single overhead camshaft is a type of engine that only has one overhead camshaft. But what does this even mean?
This means that the head of this engine has one camshaft on top. But this is strange, how is the camshaft on top of the engine?
Yes, it is a bit strange if you are coming from a pushrod V8 engine that had the camshaft in the core of the block. This old design works differently compared to modern engines that have camshafts on top of the engine instead of in the engine core.
Placing the camshaft on the top of the engine made engines much more practical and carmakers were able to fit a lot more horsepower in a smaller package.
This new design also improved the efficiency of the engine as well as the gas flow, resulting in greater power output by the engine.
The SOHC is one of the oldest configurations when it comes to overhead camshaft design and it only implements one camshaft and is running two valves per cylinder. One of them is the intake valve and the other is the exhaust valve.
This simple design made the engines much more affordable and easier to maintain. Since there are no pushrods in these types of engines and all of the engine work is run by a timing belt or a timing chain. More about the timing we are going to cover later after we elaborate more on DOHC and see which is the best when it comes to SOHC vs DOHC.
What Is DOHC?
DOHC is a similar engine design to SOHC. The difference between the two is that the DOHC engine has double overhead camshafts. Which means everything times two.
This makes double overhead engines quite more expensive and difficult to maintain and repair. Since there are more parts involved inside them.
But the benefit from this design is that there is more power. Since there are two camshafts on the head and two valves more per cylinder. This means that this engine will deliver more power for the same displacement.
This power increase also puts some stress on the block of the engine and means that the engine block will run for fewer miles compared to a block with a single overhead camshaft design.
Not to mention that the DOHC engines have a decreased fuel efficiency and they waste more money on gas. This will result in more frequent visits to the gas station to fill up your tank. And this for some people can be a deal-breaker since all that they want is a reliable commuter that is spending less fuel.
Most people do not have a high-performance street machine that will rip off the tarmac. That’s why some people still insist on driving the good old SOHC engines.
But that doesn’t mean that DOHC is bad. DOHC is actually quite good on modern cars and the DOHC engine brings a lot of reliable performance to the table. Since cars these days become a lot chunkier, SOHC engines do not have the right power anymore to move these cars.
That’s why when considering SOHC vs DOHC. Getting a DOHC engine will be a good idea. You will have an increased power delivery and a lot more performance on the table.
Engine Timing
Engine timing is a big deal when it comes to SOHC and DOHC engines. This is the case because the camshafts are driven by the crankshaft.
All this is made possible by using timing belts on the engines or timing chains in some applications. The timing chains are fairly inexpensive components but replacing them is pretty complicated. But why is this the case?
This is the case because overhead camshaft engines are interference engines. This means that the camshaft position plays a big role in running the engine properly.
If the camshafts are rotated wrong when installing the belt. There could be some major engine damage.
In the best-case scenario, you will only have to replace a few valves. This is the case because the engine valves and the crankshaft should have the right timing in order not to collide.
When they collide, there is carnage inside of the engine. The valves will get tweaked and the pistons will be damaged as well. In some cases, even the cylinder walls get damaged as well. This will result in thousands of dollars spent on repairs. In some cases, even a new engine will be required. That’s why you need to make sure that the timing is right when you replace the belt.
If your belt needs replacing, then the best option for you is to visit a mechanics shop and replace the belt there. I’m saying this because even if you make a mistake even just an inch in the timing. It may result in permanent engine damage.
The best thing to do is to go to a shop and let the technicians over there tackle the problem. This job requires a lot of experience in understanding SOHC vs DOHC and that’s why you cannot risk any chances.
Timing Belt Vs Timing Chain
Before we dive deeper into the SOHC vs DOHC and the advantages and disadvantages of these two designs. Let’s first see what is a timing chain and what is a timing belt. These two components are often confused and many people think that they are the same.
They basically do the same work. Just the philosophy of their design is substantially different. The timing belt is designed to be a cheap and extremely affordable component.
The timing belt is manufactured out of Kevlar and is covered by rubber. This makes the belt extra durable and able to withstand a lot of stress. Belts usually last between 50,000 to 60,000 miles with no issues whatsoever.
But as soon as they reach the mileage or they start to age. The belt will start to develop cracks and these cracks will be more and more obvious as the belt is deteriorating. If the belt is not replaced on time. The belt will simply snap into pieces and cause engine damage. That’s why you should pay attention to when you swap your belt.
Timing chains on the other hand work differently. They are located inside of the housing where they could get proper oil lubrication. They need to be lubed because they are metal components and if there is no lube inside of them, they will wear off.
Timing chains last longer than regular timing belts and do not snap. Though, they can develop rattles and will start to make noises when they are about to go bad.
Also, the tensioners on some engines can break more often. The tensioners are plasticky bits that are holding the tension on the chain. Overall, much safer alternative than belts. But what about SOHC vs DOHC? Let’s see.
SOHC Advantages Over DOHC
Now it’s time to discuss more about the advantages and disadvantages of these two designs. Since there is always an upside and a downside when you are buying something.
We need to make these things clear for you to make a good purchase and not to regret it later. That’s why we are going to list the advantages of SOHC and then we will cover the DOHC engine. Lastly, we will sum up, and see which is better than the other. So let’s elaborate on the reasons why SOHC is better and which are the advantages that it offers.
Cheaper To Maintain
The number one reason why you should get SOHC instead of DOHC is that the SOHC engine is cheaper to maintain. Why is this the case?
This is the case because the SOHC has fewer components. One camshaft less and two valves per cylinder less.
Imagine that you need a valve job. You will have to pay twice for a DOHC compared to a SOHC engine that only has one intake and one exhaust valve.
That’s why SOHC is better in this comparison. Another comparison is the camshaft. One less camshaft can mean a lot. Since some engines like Honda, for example, are notorious for eating through camshafts. That’s why this is another plus for the SOHC engine.
And the last thing is the price of the head as a unit. A DOHC head is much more expensive to manufacture and if you need to replace the engine head. You can expect to pay a lot more to replace a DOHC head compared to a SOHC head.
More Fuel-Efficient
Although many will claim the contrary that DOHC engines are more fuel-efficient this is not true. Since you have double the valves and power. It is highly likely that there will be a loss in fuel efficiency.
That’s why SOHC engines are considerably more fuel-efficient compared to DOHC. Less number of valves means less fuel injected. Less fuel burnt, equals better fuel economy.
A SOHC engine has more than 30% fuel-efficient combustion than DOHC. Although DOHC is making considerably more amount of power since it has more valves. These are the upsides and downsides that you will experience with either of these types of engines. One is higher in power while the other is more fuel-efficient.
So, when you consider which one to get if you have the option for a SOHC and you want to save some money on gas. This is the way to go. DOHC will work, but you cannot expect it to be a very efficient engine.
More Reliable
SOHC is also more reliable than DOHC. But why is this the case? SOHC implements one camshaft. The camshaft is a lot chunkier and pretty hefty compared to camshafts on DOHC engines.
This will result in longer life of the camshaft. It will suffer less wear and tear and will last considerably more than a DOHC camshaft. Camshafts are also expensive and if you are running an engine that eats through the camshafts, you can expect a considerable large amount of money to get it replaced or refinished.
Not to forget the valves. When we mention SOHC vs DOHC we also want to point that SOHC has double less the number of valves than DOHC. This will result in less wear and tear on the valves. Bigger and heftier valves will also improve combustion as well.
When the valves fail, it is much simpler to do a valve job on a SOHC than on a DOHC. Resulting in cheaper repairs and saving a ton of money in the long run. That’s why if you are into reliability SOHC is the engine for you.
DOHC Advantages Over SOHC
SOHC has many advantages over DOHC, but also DOHC isn’t lacking a lot when it comes to the advantages over the SOHC design. That’s why, before you consider getting a new car, you should consider DOHC as well. In this chapter, we are going to cover all of the advantages of the DOHC design and see where it outperforms the SOHC. Let’s elaborate.
More Power
If you are on the search for a high-power engine. Then DOHC engine should be one of your top picks. But why is this the case, what makes this engine so powerful?
The DOHC implements dual overhead cams and double the valves. Which means bigger combustion and also bigger injectors on these engines. More fuel dumped into the engine will result in higher horsepower.
A DOHC gets more than 30% more power compared to the SOHC and this is quite a lot when you want to run a high compression engine. For example, if you equip a Toyota Supra 2JZ engine with a SOHC head, it will not make not even close the amount of power that is made with the DOHC-designed head.
That’s why high-performance engines are implementing DOHC design and their only goal is to deliver a lot of performance on the table. So, when it comes to power SOHC vs DOHC, the win takes the DOHC by a big margin. If you want to make a high-performance application, go for the DOHC without even thinking twice.
Decreased Emissions
One of the reasons why DOHC engines were put into mass production was the claims that they have decreased emissions. Maybe with the improved combustion, they have a better performance overall and burn off more harmful particles than SOHC engines.
They have also decreased emissions but not by a big margin. Even though most of the recent cars are DOHC and they also are packing advanced EVAP systems, catalytic converters, and other emission control systems. They can be considered to be a cleaner option if you want to get an engine that is polluting less.
Smoother Engine
DOHC engines are also running quite smoother than SOHC. This is the case because the balance of the engine is quite improved when there are two cams on top of the head instead of one. The engine doesn’t move a lot and runs considerably smoother. If you have a DOHC engine, you are going to save a considerable amount of money on engine mounts and other components.
If you want a DOHC and you aim to get a smooth-running engine. The best option would be to get a straight-six engine. Six cylinders work better than 4 or 3 cylinders. The smaller number of cylinders, the less balance the engine has, the more vibrations it produces. Bigger displacement engines maybe are not good on fuel, but when it comes to performance, they outpace almost anything out there that has 3 or 4 cylinders.
But what about SOHC vs DOHC? That we are going to cover in the next chapter where we will give out opinion on which engine to get.
SOHC vs DOHC – Which One To Choose?
When considering between SOHC vs DOHC it is important to learn your need first. Since both types of engines are similar but perform quite differently and have different characteristics.
For example, if you are on the market for a good and reliable engine that is economical and does not drink a lot of fuel. Then the SOHC design would be the perfect car for you as your next daily commuter.
As we mentioned, SOHC has double less the number of valves which in other words translates into less fuel spent.
DOHC on the other hand although is more performance-oriented in its early inception, it became a standard in today’s world and the vast number of cars that are manufactured each day are DOHC.
They drink more fuel. But on the other hand, they deliver considerably more amount of power to the table. That’s why if you want to have a good car that pulls, this is the way to go in my opinion.
So, to sum it up really quick. If you want fuel economy go for SOHC, if you want performance and pulling power go for DOHC.
How To Tell If My Engine Is SOHC Or DOHC?
There are two ways that you can check if your engine is SOHC or DOHC. But what are these ways? How can you tell what type of engine you are having? Let’s see.
The first way is to check the specs of the car. You can do it by checking your driver’s manual or going online and Google your car and your engine then SOHC vs DOHC and you will probably get a good result that will explain everything you need to know.
Or use the simple method. Open the hood and check the belt. If there are two pulleys on top of the engine it means that this engine is DOHC. If there is only one pulley it means that this engine is SOHC.
Usually, DOHC engines also have a bigger and wider head as well. So, it’s pretty easy to tell.
Camshaft Setup Facts: SOHC vs. DOHC
- A camshaft is a rotating cylindrical rod with lobes that push intake and exhaust valves in an internal combustion engine.
- SOHC (Single Overhead Camshaft) uses one camshaft to control both intake and exhaust valves, while DOHC (Dual Overhead Camshaft) uses two separate camshafts.
- An OHV (Over Head Valve) engine, also known as a “pushrod” engine, uses a camshaft inside the engine block and valves operated by lifters, pushrods, and rocker arms.
- SOHC typically allows a 2 or 3 valves per cylinder configuration, but can also allow 4 valves per cylinder for better airflow.
- A SOHC 4 valve engine has better torque towards the low end due to the lesser mass of the valvetrain.
- DOHC improves volumetric efficiency, resulting in more horsepower out of smaller engine displacement.
- DOHC allows the intake valves to be at a larger angle from the exhaust valves, resulting in a more direct airflow through the engine.
- DOHC allows easy implementation of a 4 valve per cylinder configuration and allows the engine to rev higher.
- DOHC engines have more weight and higher costs due to the need for more components.
- A 4 Valve per cylinder SOHC engine with a lighter valvetrain mass would have better performance characteristics at the lower end of the powerband, while a DOHC setup would develop higher peak torque and horsepower at higher engine speeds.
Conclusion – SOHC VS DOHC
In this article, we have covered a lot when it comes to SOHC vs DOHC. We have learned what SOHC and DOHC are. Then we covered their advantages.
As we noted, SOHC is simpler to make and cheaper, also more fuel-efficient since it has a lower number of valves. DOHC on the other hand has more valves and produces more power. Making it more expensive to produce and to run.
When considering one between the two. The way to go will be the one that you need. If you are into fuel economy, go for the SOHC. If you are into performance, the DOHC is the right option for you as your new engine. Even though most cars these days are DOHC and they are mostly updated when it comes to emissions and other standards. That’s why if you want a newer vehicle, the high probability will be that it’s going to be a DOHC design.
