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Water Injection: Let’s Get to Know the Definition and How It Works

Water Injection is not something new anymore, this technology has existed since 1920, aka almost a century ago. Many technologies that were originally developed for military or space use were later adapted for more general use. Well, this water injection rose in prestige during World War II. At that time, fighter planes used it to increase engine power in short durations such as during take-off or close combat (dogfights).

In the automotive world of cars, water injection is then applied in the motorsport purpose especially in drag or rally . But not only for racing, this technology is also used for mass production cars (production car). These cars are equipped with a forced induction system that does get significant benefits from water injection. For example a BMW M4 GTS with a 3.0 L twin turbo engine capable of spewing power at 493 hp, in contrast to the normal M4 with the same engine that has a power of 425 hp.

Previously we have reviewed the technology of raising other engine power such as turbochargers and NOS / Nitrous Oxide . Now, we will discuss this water injection in full. Starting from the understanding, how to work, advantages and disadvantages, and others.

Are you ready for the coffee?

What is Water Injection?

Imagine the presence of water in the combustion system on the engine is certainly very scary. This usually happens when the car is flooded so that water enters through the intake into the combustion chamber. The result is a hydrolock whose effect is very damaging namely the destruction of the engine’s interior.

Well, this water injection works by injecting water into the engine combustion chamber.

Are you dangerous?

No. The intensity of the water used in water injection is so small that the movement of the piston is not affected by the presence of the water. Water that is injected is in the form of mist, not liquid flow, so that it evaporates quickly enough in the combustion process.

The main use of water injection is for the cooling process. Unlike the coolant that cools the engine from the outside, water injection cools the engine from the inside. Water is injected at a precise timing when the piston is compressed. On machines with high compression which are identical to machines with large power, the phenomenon of pre-ignition often occurs . High compression sometimes causes hot spots in the cylinder so that the air-fuel mixture burns first before the spark plug ignites. This in the long run can be fatal for the engine. Turbochargers and superchargers with large (and hot) air boost or compression are also prone to pre-ignition.

Although the current knocking sensor (knock sensor) is more sophisticated to detect and overcome pre-ignition, the results still reduce power and fuel efficiency. With the water mist entering the cylinder, heat during compression can be transferred with cold water mist. The result, a high turbo compression or boost engine is safe from pre-ignition.

Water injection is done on the intake system which makes the air at the intake cooler. Cold air is more concentrated so that more volume of air can enter. The more air in, the fuel volume can be increased so that of course the power can increase.

The composition of the injected liquid is not just water. The tuners often add alcohol (methanol) which functions as an antifreeze (frozen barrier) which is also flammable. Therefore, this process is often also referred to as water-methanol injection. Sometimes too little oil is mixed with which serves as a corrosion prevention.

Mechanisms / Ways of Water Injection

Now we will discuss about the workings of water injection. This way of working is general in the sense that we will not discuss the technical details. For that, let’s take a look at the water injection video from the BMW M4 GTS.

  1. At 40 seconds we can see a turbocharger engine that is working normally (RPM below). Turbochargers are not very active at work, the compressed air is still normal (depicted blue air flow).
  2. At 45 – 1:03 seconds, the turbo turbine starts to increase its rotation, from blue to yellow. This is a sign the driver starts pressing the accelerator. Compressed air gets bigger and starts to heat up (turns yellow). However, thanks to the intercooler, the rather hot air can still be cooled (again turned blue). This cold compressed air is then channeled to the cylinder along with the addition of fuel so that power begins to increase.
  3. At 1:04 minutes, the turbo spin is higher, from yellow to red. The driver presses the accelerator even deeper (high RPM). Compressed air gets bigger and hotter (turns red). Even after going through the intercooler, the hot compressed air is not so cold.
  4. When the high RPM conditions and hot compressed air, we can see at minute 1: 08 water injection becomes active. Water begins to flow from the tank behind the car.
  5. Water mist injection is done at the intake after intercooler, before entering the engine cylinder. The rather hot compressed air turns into cold compressed air.
  6. The final results are now visible. The turbo compressed air is red (hot), through the intercooler to yellow (warm) then thanks to water injection it turns blue (cold) again.
  7. Cold air is more concentrated so that more volume of air can enter. The more air in, the fuel volume can be increased so that of course the power also increases.

Please note, the video demonstration above runs at an accelerated pace. Like a machine that is working. Therefore, the injection of water mist appears as if it is spraying continuously. When in fact this injection runs in one spray, as well as air and fuel in the cylinder. For more details, we can see in this video .

In addition, at minute 1:23 we could see that there were 3 injectors used to inject water mist. The use of injectors more than 1 is intended to anticipate the occurrence of malfunction. So if one of the injectors doesn’t work, the water injection system still works.

Advantages and disadvantages of water injection


  1. Prevents pre-ignition on high turbo compression / boost engines.
  2. Cools the intake so that it can increase the amount of air & fuel, the results of which will increase power and torque.
  3. Improve fuel efficiency.
  4. Reducing the amount of emissions from combustion exhaust gases such as NOx and carbon monoxide.


  1. Water injection timing settings are very critical. A precise tuning is needed so that the water injection can work precisely. The wrong results can make the engine even lose power.
  2. The amount of water that is too large either because of a wrong setting or a problematic injector (malfunction) can be fatal. This too much water cannot be compressed, causing engine damage like hydrolock.
  3. The sudden stopping of the water supply, either because the tank is running out of water or the damage to the injector can have a bad effect. This is because the ECU has been setup to adjust to the addition of cold water mist. A good water injection system will have a fail safe mode When the water stops, the mode will work to reduce engine power for example by reducing the boost on the turbo.

Tips and Other Things About Water Injection

  1. With the presence of intercooler devices, water injection technology has become somewhat irreplaceable. Moreover, the settings do add to the complicated engine system. Nevertheless, the effect of reducing emissions remains a special advantage of water injection. Besides the turbocharger / supercharger compressed air can get even cooler. Therefore, some manufacturers and tuners often keep installing these two devices for maximum results.
  2. Be careful with unreliable Water injection kit products that only spray water fog. Without ECU tuning or special modifications to the engine to adjust the timing ignition , the results will be in vain or may even damage the engine.
  3. Injecting air mist in the intake system can cause rust on the connection, bolts, clips or other intake components. The rust will be dangerous if it enters the engine room. Check the component and replace it with rustproof material.
  4. Similar to a water injection system, water can also be sprayed on an intercooler. This is also called the Intercooler Water Spray . Its function is to reduce the temperature of the intercooler so that the compressed air can be even cooler.

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