Thanks to the use of multiple valves which pumps in more air-fuel mixture into the cylinder, the engine breathes better which in turn translates to lesser unburnt fuel or emissions and higher efficiency. Furthermore, since multiple valves are smaller in dimension and lighter in mass compared to a two valve configuration, they travel freely and at a higher frequency, enabling the engine to run at higher rpm and extract more performance.
A secondary benefit to having a four valve, twin cam setup is, it gives engineers the flexibility to position the spark plug on top of the cylinder for optimum flame font and better combustion. However, on rare occasions, the spark plug has to be moved to the side in the case of a multi-valve single cam setup.
That said, a four valve engine does have a couple of drawbacks. The use of multiple valves requires more space in the cylinder head, which leaves for fewer tolerances and weakens the overall structure. The only workaround for this is to use top quality materials in order to strengthen the cylinder head, which in turn makes the process more complex and pushes the cost of manufacturing.
Hence, they are expensive to replace and maintain. Two valve engines are typically used on budget-friendly or commuter motorcycles. As the name suggests, there are only two valves operated by a single overhead camshaft SOHC. The largest valve of the two takes care of intake while the smaller valve is responsible for discharging the exhaust gases.
Thanks to the simple construction, they are simpler to manufacture, easy to maintain, and hence the more cost-effective solution. It contains a piston that moves up and down, compressing the fuel, which ignites and causes combustion. There are two valves at the top of the cylinder; an inlet valve and an outlet valve. The inlet valve is where the fuel and air enter the cylinder from the carburettor or electric fuel injector, and the outlet valve is where exhaust gases escape.
The exhaust gases created during combustion in the cylinder rotate an axle known as the crankshaft. These are connected to the bottom of the cylinder which in turn powers the gearbox that drives the wheels. The more cylinders there are, the more pistons are combusting the fuel, and therefore more power is generated. Cylinders can be laid out under the bonnet in a straight line, in two rows or in a flat arrangement. Engines with cylinders in a straight line are known as an inline engine i.
I4 or L4. These usually have less than six cylinders. Those in two rows are referred to as a V engine, as they are usually in a 'V' formation and have more than six cylinders. UK Engines with a flat arrangement generally have four to six cylinders. Another important performance aspect associated with the four valve geometry is the flexibility to position the spark plug on the cylinder head.
Position of the spark plug on the cylinder head is a very important for optimum flame propagation. But with the four valves setup, there is sufficient space to place the spark plug in dead centre of the cylinder head, allowing for better spark propagation and more efficient combustion. More valves also provide additional cooling to the cylinder head, which allows the engine to perform without heating up for longer durations. Now, as you have seen, the advantages of three or four valve cylinder over their two-valve counterparts are many.
Here are a few of the advantages a two-valve configuration has, which makes them relevant even today. A two-valve per cylinder layout is simple and cost effective. To get a four-valve layout right from a metallurgy and thermodynamics perspective is way more difficult than a two-valve setup. The complexity associated with a four-valve system also leads to escalation in costs. Thus, four-valve engines are considerably more expensive and are not always the most suitable option for a price-sensitive market like ours.
Finally, in some cases, the design of a two valve per cylinder engine tends to facilitate better low and mid range torque as the air flow is restricted. This, however, is negated by 4 valve engines which have variable valve timing. We hope this article dispelled any doubts you had about two, three and four-valve engines. Also, do not forget to share this informative article with your friends who you think would benefit from it. Home Media Blog Blog.
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