If you’re an automobiles-and-mechanics enthusiasts, then you probably have a good idea of the various types of engines and how they work. For those of you who are just about getting initiated to the exciting world of automobile technology, before we proceed towards dismantling and taking a detailed look at what a DOHC engine is, let’s first familiarize ourselves with seven crucial terms – cam, camshaft, valvetrain, cylinder head, combustion chamber, tappet and poppet valve. You must be wondering why I am conducting a session on automobile engine jargon when I should be discussing DOHC engine. Well, all these are various parts of an engine that form important parts of the entire picture of overhead camshaft valvetrain configuration which one must be familiar with if he/she is to fully understand a DOHC system of automobile engines.
A cam is a part of a mechanical linkage which rotates or slides to alter a linear motion into rotary motion or the other way round. The shaft to which a cam is attached is known as a camshaft. A tappet is a part that juts out and causes another component within a specific mechanical assembly to experience linear motion. A poppet valve is composed of a shaft upon a disc-shaped base supporting a tapered plug with a hole through which the shaft passes all the way to the top. The hole of the valve may be round as well as oval. A cylinder head is that part of an internal combustion engine which is positioned on top of the cylinder block, just above the cylinders. A combustion chamber, needless to mention, is where the engine burns the fuel. A valvetrain includes all those components and mechanisms that are involved in controlling the operative functions of valves within an engine.
What is a DOHC Engine?
Now that you are aware of the various parts and components involved in a typical overhead camshaft configuration, let’s understand what an overhead camshaft valvetrain is. In such a configuration, the cylinder heads cover the camshaft which is placed over the combustion chambers. This allows the camshaft to directly control the tappet or valves. This makes it different from overhead valve (OHV) pushrod systems. An engine possessing an overhead camshaft valvetrain configuration can either be a single overhead camshaft (SOHC) engine or a double overhead camshaft (DOHC) engine. In a double overhead camshaft engine, there are two camshafts within the cylinder head. Now, your next question must be ‘how does a double OHC engine work?’, right? Well, the two camshafts work by dividing the operation of the intake and the exhaust valves among themselves. While one camshaft controls the operation of the intake valves, the other regulates the functions of the exhaust valves. Engines which involve multiple banks of cylinder heads may use more than two overhead camshafts. However, they are still called DOHC engines.
Advantages of a Double OHC Engine
So what could be the advantages of using a DOHC over a SOHC engine? Well, firstly, you’re getting 4 valves per cylinder where a DOHC configuration is involved, as opposed to 2 valves per cylinder of SOHC engines. This means that DOHC powered engines allow increased air circulation inside and outside the cylinders, resulting in better engine performance. Secondly, this increased airflow directly affects the performance potential of an engine, especially in case of accelerated revolutions per minute.
However, there are some gray areas vis-à-vis an argument of whether or not a double OHC engine is a better option compared to a SOHC engine. Most people agree that a well tuned SOHC engine can be as efficient as a DOHC variant engine and many cases of DOHC variant engine automobiles performing better than SOHC engine automobiles have other factors also whose involvement are as responsible for performance as the number of camshafts. Better engineering could be a big reason. Many people also argue that SOHC engines provide higher revolutions per minute and pack more torque. However, an overall verdict is that as far as power of the engine and performance is concerned, a DOHC variant engine packs more punch than a SOHC engine, any day.