A Comparative Analysis of Various Valvetrain Types
A car’s engine consists of literally thousands of parts. They may be big and heavy or something very small, less than the size of an almond. However, each of these parts has an important use in helping your car run properly and as efficiently as possible. One such part is a valvetrain.
But what is a valvetrain? Put simply, a valvetrain, as the name suggests is a series of valves. Specifically, each cylinder in a car comes with two valves — an intake valve that opens and allows the fuel into the cylinder, and an exhaust valve that opens and allows the exhaust gasses out of the cylinder. Both valves work in tandem with the piston which is constantly moving up and down within the cylinder. Now there are several types of valvetrains. But what are they and how are they different from one another?
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A Background
Now, before we delve into the details of valvetrains, there are a few engine parts that you need to familiarize yourself with to better understand how a valvetrain works. You see, none of the engine parts work independently of one another. There is an entire symbiotic relationship going on under your hood. To understand valvetrains and their functions and variations, three engine parts must be taken into consideration:
- Camshafts- As the name suggests, the camshaft is essentially a shaft but it also has precisely machined lobes on it. The camshaft is always in sync with the crankshaft that is connected to the piston which are located in the cylinders. The lobes on the camshaft control the valves on the cylinders as the camshaft is in constant rotation. The number of camshafts differ from engine to engine depending on the number of valves and the engine design.
- Push Rod- It is a rod used to connect the camshaft when the latter is located within the engine block. The lobes are connected to rocker arms that help in the opening and closing of the valves.
- Timing Belt- Timing Belts are belts that connect the camshaft with a drive spork which is connected to the crankshaft. The belt decides the precise time to turn the camshaft depending on the crankshafts’s cycle allowing the valves to open and close at the optimum time for the best efficiency and performance.
These three engine parts play a vital role in deciding how the valvetrain functions. If these parts malfunction, the valvetrains will do the same having disastrous results for the engine and performance.
Now, coming to the type of Valvetrains:
Over Head Valve (OHV)
The biggest difference between the OHV valvetrain as compared to any other form of valvetrain is the fact that in this case the camshaft is located within the engine block instead of over it. To help work on the valves, there are instruments called pushrods which are connected to a rocker arm. This makes the system slightly heavier and stops the engine from running at higher RPMs. The advantage of this system is that the design is a lot more compact and simpler in terms of lubrication. The lobes on the camshaft come in connection with the pushrods which operate the rocker arm that is connected to the valves.
Unfortunately, this system has a lot more disadvantages than advantages. Due to the higher number of components, these engines have a lot more friction and noise, any issues with the camshaft require the entire engine to be taken apart which makes it more difficult to maintain and repair, and the higher number of components also makes the engine heavier even though it cannot be compatible with higher RPM engines.
Single Over Head Camshaft Valvetrain (SOHC)
Unlike in OHV valvetrains, for the SOHC valvetrain, the camshaft is located directly above the cylinders. These camshafts have the same lobes, except they come in contact with the valves directly rather than through the pushrods and rocker arms. A single camshaft does the work of both valves, the intake and exhaust. The Camshaft is connected directly to the crankshaft through the timing belt to ensure that the valves are in sync with the motion of the pistons within the cylinder.
In this case, the valves have springs that keep the valves closed until the lobe of the camshaft comes along and opens them up. While these have a significant advantage of simplicity and ease of maintenance over OHVs, and can also run on higher RPM, one disadvantage is that this system is ideal for two to three valves per cylinder at max. If you want another valve, like a 4-valve-cylinder, the mechanism becomes much too complex
Dual Over Head Camshaft Valvetrain (DOHC)
The setup of this system is quite similar to the SOHC system. Except here instead of one, there are two camshafts working simultaneously. These are most commonly seen in V-engines like the V6 or V8s. In such cases, the car will have a total of 4 camshafts, 2 for each side of the V, and on each side, one camshaft will focus on the intake valve while the other will focus on the exhaust valve. This also allows the spark plug to be put right in the middle of the valves allowing better explosions within the engine.
The DOHC system comes with quite a few advantages for example it helps the engine breathe better, it can also handle variable valve timings for the engine, and can handle high RPMs as well. This type of engine is predominantly best suited for performance and sports cars. However, this system has some disadvantages as well, like the weight of the extra camshafts and slightly more complicated engine production and maintenance. It is quite unnecessary to have this system in cars that are mostly meant for cruising and driving around, in which case the SOHC system is a far better fit.
Flathead Valvetrain
Although this system is old and is not used anymore, it is worth mentioning as most classic cars have this system. The Flathead system is also known as a side-valve engine or a valve-in-block engine. In this case, the combustion chamber and the valves are located within the engine block which end up in a relatively flat cylinder head. The valves are positioned within the engine block beside the cylinder instead of being placed in the cylinder head. Unfortunately, this system while being nostalgic, still has some limitations. Unfortunately, these systems were not the most efficient or powerful and neither were they able to carry out combustion in the best possible manner
This system did not need many of the components modern-day engines use for their valves like pushrods, rocker arms, overhead valves, and overhead camshafts. This system is still used in marine technology and small engineering manufacturing units. The only cars that use this system are classic cars and hot rods.
Final Thoughts
While Flatheads came into being much earlier than the camshaft designs, it had its limitations. As of today, there are three options one can go for when it comes to different types of valvetrains. Each valvetrain has its own set of advantages and disadvantages. However, the valvetrain your car comes with specifies what you can expect out of the car. Coming to the question of which is the best? Well, it’s hard to say. In all honesty, if you want a fast car running at higher RPMs then it’s best to go for the DOHC, a low grunt torque engine will run quite happily with a SOHC while an old passenger hatchback will have an OHV although the newer cars have a higher chance of coming with a SOHC unless it is necessary for a DOHC.
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