Why are four-valve cylinders better than two-valve ones?

Why are four-valve cylinders better than two-valve ones? Before answering this question, we must bear in mind that, for engines, air is power, and the additional valves draw in much more air into the cylinders.

As experts confirm, multiple intake and exhaust valves improve driveability and even performance.

Today, engines with four valves per cylinder are the norm. Engines with two valves per cylinder are a thing of the past, because it has been shown that vehicles perform better with those “two extra valves per cylinder”.

It is important to point out that the operation of the engine depends on the amount of air that each cylinder can ‘draw in’ in order to produce energy. Surprisingly, using two large valves, one to let the exhaust gases out and a larger intake valve to let air and fuel in, is not the best way to do it.

Four valves per cylinder better than two

Do the numbers surprisingly reveal that two smaller valves, say, half the size of a single valve, allow more air to flow into the engine? The power an engine produces derives from the torque generated in each combustion cycle, so up to a point, the faster an engine accelerates, the more power it will produce. But at high revs, it becomes harder to draw in enough air quickly, and that is where two intake valves have an advantage over one.

The addition of extra valves also gives designers more room to improve the swirl in the combustion chamber, which is necessary for mixing fuel and air, and smaller components are lighter, which is an advantage when they have to move faster. The downsides are that four-valve designs require many more parts and more complex machining than two-valve ones, and in the past that restricted the use of the design to more exotic engines.

The idea is not new; it first appeared in cars at the beginning of the 20th century. Honda split the difference in the 1970s with the three-valve-per-cylinder engines of the Civic, two intake valves per cylinder and one exhaust, which delivers most of the advantage of four valves, but uses only one camshaft to keep costs low.

The more recent major development has been direct injection and the insertion of an injector into each combustion chamber, as well as a spark plug. With direct-injection engines, more of the combustion chamber sits in the crown of the piston to generate maximum swirl and the best mixture of air and fuel, but the design of the cylinder head intake ports remains important.

Therefore, although most modern engines are generally driven by turbos, cooling an engine still plays an important role.