Okay, you might argue, “why do I need to know this”. Let me tell you, Bajaj Pulsar 200NS has 4 valves per cylinder whereas Yamaha FZ25 has two. So, this is a valid conundrum that you might face while buying a bike. Whether to go for Single valves or multi valves?
So, without going much into the technicality of this aspect, in layman’s term, we will tell you which is used and for what purposes.
What is a camshaft?
Camshaft, is a shaft! If you look at the image above, part marked 1 is a camshaft. And part marked 2, are the valves. Valves are connected to the camshaft. The camshaft is responsible for opening and closing of valves and the timing of it. Timing is essential here. If you look closely, there are two lobes, each connected to a valve. When the camshaft rotates, the shape of lobe determines the timing of opening and closing of valve.
Single Overhead Camshaft (SOHC) means, there is only one camshaft, whereas Double Overhead Camshaft (DOHC) means use of two separate camshaft for intake and exhaust valves.
Single And Multi Valve Configuration
A SOHC uses a single camshaft to control both the intake and exhaust valves. Intake valve, takes in air fuel mixture into the combustion chamber, spark plug ignites the air-fuel mixture and then exhaust valve facilitates exhaust gases to come out of the combustion chamber. A DOHC uses two camshaft. One for intake valve and another for exhaust valve. So, both the valves are controlled by separate camshaft. So, they can be timed separately.
Advantages of having two or more Camshafts!
The first advantage is, taking a large single valve and breaking it into two smaller valves of half its radius, increases the air intake capacity by 50%. Which means, the engine breathes better, and it results in less emissions and greater efficiency.
As the valves are smaller now, the travel more freely and at higher frequency, enabling the engine to run at higher rpm and extract more performance. Note, the engine can now run at a higher rpm resulting in greater top-end power. So bikes use single cam setup, like Harleys, to produce greater torque at lower rpm.
Multiple intake valves allow the engineers to set slightly different valve timings. So that valve works differently and different speeds. For example, providing richer fuel at higher speeds. Thus it helps in optimising engine performance.
Like every good thing, it has its drawbacks.
Use of multiple valve cylinders might be efficient, but it is very complex to design and produce. Four-valve engines are considerably more expensive and are not always the most suitable option for a price-sensitive market like ours.
In some cases where more torque is required at lower rpms, use of single camshaft is required. This can be overcame in four valve cylinders by having variable valve timing, for lower rpm and higher rpm.
It doesn’t mean that “one thing is right and the other thing is wrong”. Like I said, it depends on your goal. When the goal is high revving power, then you should look at four valve or Dual Overhead Camshaft (DOHC).
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