What’s the working principle behind a multi-valve engine?

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A four-stroke burning engine requires the air-fuel mixture inside the combustion chamber to burn well to provide a decent amount of power and deliver great fuel efficiency. The valves allow the air-fuel mixture to enter the combustion chamber. Naturally, then, if the intake valves allow a more robust flow of air into the combustion chamber, the engine would be able to breathe better, with more efficient burning of fuel.

To explain this mathematically, picture the valve on a two-valve engine as one, large circle, and also the intake valves on a 3 or four-cylinder engine as two smaller circles. Now, the number of air that these valves can let into the combustion chamber is mathematically represented by the wall area of the imaginary cylinder that’s formed when the valves are pushed inside. If the travel of the valves altogether cases is that the same, say X, we’d like to try to to the subsequent math.

Assuming that the radius of the massive single valve is 30mm, which of the 2 smaller valves is 15mm each, let’s see the difference in the air inflow. The formula for the extent of the imaginary cylinder through which the air will flow – 2*pi*R*X,

  1. pi is that the ratio of a circle’s circumference to its diameter, or 22/7 or 3.14159
  2. R is that the radius of the circle, or the valve, in this case
  3. X is that the travel of the valve
  4. Airflow area for 2 valve per cylinder layout: 2pi30X = 60piX
  5. Airflow area for 3 or four valves per cylinder layout: 2pi15X + 2pi15X = 90piX

As you’ll see, by increasing the number of valves, the air intake capacity of the engine went up by 50% (60 Vs 90). So mathematically, breaking an oversized valve into two smaller valves of half its radius would end in 50% more airflow into the engine.


Inlet and Exhaust Valves:

Now, of the inlet and exhaust valves, the priority is usually inlet valves, as it’s always harder to let more air into the combustion chamber than pushing it out. This keeps the engine design relatively simpler, and enhances the engine performance to an extent, without pushing the value up an excessive amount. This sort of valve design is named a three-valve per cylinder configuration and does an honest job of balancing the performance to cost ratio.

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