If you have been looking for a new car and if you have been looking at the engine specifications, you have probably seen that there are often specs like SOHC or DOHC.
But what do these signs mean? Both terms are used in regards to the camshaft. There are some significant differences between these two types of setups.
Before you decide if you should choose a DOHC vs. SOHC engine, you need to understand what they mean and how they operate. Let’s begin
SOHC VS DOHC – What is the difference?
The difference between the SOHC vs. DOHC engine 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
- DOHC = Dual Overhead Camshafts.
The engine is most often run 2 intake valves and 2 exhaust valves per cylinder with DOHC engines, instead of 1 intake and 1 exhaust valve on the SOHC engine. 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:
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.
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. The camshafts are often tied together by a short chain but sometimes, the timing belt wrap around both gears.
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Which should I choose – DOHC or SOHC?
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 actually 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 properly.
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 greater 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 important to you – you should choose a DOHC engine.
SOHC & DOHC FAQ
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.
Levi Wrigley
I'd like to warn anyone here this isnt true in all cases. While i do like dohc engines, the argument you give is that twin cams have more valves per cylinder, but this is completely dependant on engine design NOT the amount of camshafts! for example honda D-series engines are nearly all sohc inline 4 engines equipped with 16valves. 4 valves per cylinder exactly like its dohc counter part. this is not a critism just what i have found from own experience/thoughts. if you can give another reason that twin cams are better i would be really interested to know. thanks
Magnus Sellén
True, I didn't know that. Never worked with these engines, but it's an exception then because most engines with a single camshaft only have 2 valves per cylinder. In this case, I agree it's better with a single camshaft also
Rodrigo Arcangelo
Not that common of an exception, my frist car was a nissan almera and it was SOHC 16 valves, I now have a honda accord with a F series engine and again SOHC 16 valves
GÅ-TOOLA
Pro with Sohc = if belt snaps, the motor will likely just turn off. With Dohc you're eitther expecting a total engine rebuild or a new engine.
Jake Greene Jr
It doesn't matter. In either case you are going to crush the valves that are extended into the combustion chamber as the car comes to a halt. Remember that the crankshaft is still rotating with car motion and in gear, which means the pistons are still moving up and down. Any valves in the open position are protruding in the cylinder.
Alfi Garbrah
Kindly give a VERY SIMPLE ANSWER DOHC 3.0 n SOHC 3.0. Which is faster ? I want to replace my Mercedes 603 engine with its successor OM 606 My reason being I want more speed n less noise
Kevin Ortega
Very helpful keep up with passing on your knowledge it forsure gets us people getting what we need to know to be successful and correctly provide descriptions of how it all operates as simple as it gets. No amount of "thank yous" could ever mean how truly grateful i am for pages like this and people that care enough to make it a little easier for beginner mechanics and gear heads or just simply getting another take from 1 to another experienced car enthusiast.