DISADVANTAGES OF WATER INJECTION

There are some disadvantages to using a water injection system, some of which can be catastrophic! Firstly, a failure in your water injection system would mean a complete lack of detonation suppression, which could quickly lead to engine failure! To prevent such a scenario, you need a failsafe system that will cut engine power when the intake charge temperature downstream from the water injector reaches a certain threshold. Secondly, the minerals in tap water will quickly clog up the water injector and will result in a failure to deliver the correct amount of water.

For this reason you should use distilled water in your water injection system. As with any other system, you need to ensure that only quality hoses and clamps are used in order to ensure the reliability of you water injection system.

Finally, determining the correct amount of water that needs to be injected can be pretty tricky as you do not want high boost pressure with too little detonation suppression! The safest way of reaching the correct amount of water injection for a particular application is to start with a lower boost pressure and slowly increase boost pressure. If detonation occurs, back off immediately and increase the water injection if a greater boost pressure is required.

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HOW WATER INJECTION WORKS

Atomized water rather, that vaporized water is injected into the air intake system as water only boils at 212� F at sea level while temperature of the intake charge would be much lower, having already passed through the intercooler. When water is injected into the air intake system it absorbs quite a bit a heat from the intake charge. When the atomized water, together with the intake charge, enters the combustion chamber, the high temperature of the combustion chamber causes the atomized water droplets to vaporize.

During the process of vaporization a large amount of heat energy is absorbed, resulting in anther drop in intake charge temperature! Unfortunately, vaporized water also displaces a large volume that would have been filled with air molecules, but the lowered temperature in the combustion chamber more than makes up for this loss in volume. Indeed, the lowered temperature in the combustion chamber allows us to run higher boost pressures and, consequently, allows us to make more power!

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WATER AND METHANOL

Some engine tuners prefer to inject a mixture of water and methanol into the intake system. Usually 50% methanol by weight is used. This provides the desired detonation suppression while also providing maximum horsepower. Methanol is both hygroscopic, which means it absorbs water, and miscible, which means it mixes well with water. It is also much more volatile than water, which means it vaporizes much quicker.

This vaporization further reduces the temperature of the intake charge, but it occurs before the combustion chamber is reached. Once the combustion chamber is reached, the atomized water droplets vaporize so temperatures are still reduced in the combustion chamber. But methanol is also a fuel and thus provides extra horsepower as well.

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Water Injection

On turbocharged cars water injection can also be used to cool the intake charge and reduce the possibility of detonation, though some engine tuners to frown upon it. Nonetheless, water has a very high specific heat capacity, which means it can absorb a lot of heat energy without a significant increase in temperature. As a result, water injection systems have been around in one form or the other since 1936 and were used on a variety of aircraft engines during World War II. However, water injection is only required if you're running high boost of more than 12 psi, and should be used in conjunction with a good intercooler.

The water injection system basically consists of a storage tank, a water injector, which is similar to a fuel injector, a high pressure pump, a pressure sensor connected to the intake manifold, and an intake air temperature sensor. Calling it water injection is possibly inaccurate as it can wither be pure water, preferably distilled water, or a mixture of water and methanol. Either way, atomized liquid is usually injected into the intake system when the intake air temperature is exceeding a certain value and the engine is on boost and is usually injected downstream of the intercooler.

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Turbochargers

Turbochargers

The turbocharger, or a just simply the turbo, has been around now for more than a century. It was invented by Swiss engineer named Alfred Buchi in 1905 and was first used on the diesel engines of ships and locomotives from the 1920s. It was used on the engines of production airplanes from the 1930s and on truck engines from the late 1940s. But it only found its way onto the car engine of a production vehicle in 1962 when it was used on the Oldsmobile Cutlass Jetfire.

As a forced induction system, a turbo is nothing more than an air pump that is driven by the exhaust gasses of a car engine. It consists of a compressor-wheel and a turbine-wheel that are connected by a common shaft. The compressor increases the density of the air that enters the intake manifold by forcing more air into the intake manifold than what the car would normally ingest. This higher intake air density contains more air molecules and produces more power when combined with the correct amount of fuel. This is similar to the way NOS allows more fuel to be burned by providing extra Oxygen as explained by Ian. The major difference between NOS and a turbo is that the turbo provides a constant supply of extra Oxygen to the car engine while NOS only provides a limited supply.

You've got three options when it comes to turbocharging a car:

* You can simply buy an OEM turbocharged car such as a Mitsubishi Lancer Evolution, a Nissan GT-R, a Nissan 300ZX, a Nissan Silvia spec-R, a Toyota Supra, etc.
* You can buy an aftermarket turbo kit for your car engine. Here there are many options to choose from. There are Garrett turbo kits, STS turbo kits, Turbonetics turbo kits, and so much more.
* You can also build your own turbo system, which could be the best approach to car engine turbocharging as it gives you the option to build a system that meets your performance requirements and your objectives.

A complete turbo kit consists of the turbocharger as well as the necessary parts required to bolt the turbocharger onto the car engine. This includes an exhaust manifold, intake runners (plumbing to connect the turbo to the intake manifold), and can include an intercooler as well as cooling and lubrication feed lines for the turbo. When building your own turbo system, selecting the perfect turbo for a particular application can be a real challenge as no one turbo is best suited to all applications.

There are a number of things you need to consider when selecting a turbo. These include:

* The capacity of your engine.
* The number of valves.
* At what RPM to you want the turbo to come in.
* The type of fuel you plan on using.
* The turbo boost you plan on running.
* The amount of horsepower you want.

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Turbo Basics

Turbo Basics

Approximately a ? of the energy produced by an internal combustion engine is lost as thermal energy that is fed out the exhaust manifold. It is this energy that is used to drive a turbocharger. When the exhaust gases are forced through the turbine-wheel, the turbine-wheel becomes a reduced-flow area in the exhaust system and causes some back pressure, which causes some loss in engine power. Of course, back pressure increases as the size of the turbo decreases and inversely, back pressure decreases as the size of the turbo increases. So a larger turbo causes a smaller loss in power, but it also requires more air-flow, and hence more RPM, to spin up or spool up and produce boost pressure. This is referred to as turbo lag. So a larger turbo produces less back pressure but has more turbo lag while a smaller turbo produces more back pressure but has less turbo lag. So what is better? The answer to that depends on what you're looking for � low-end torque, top-end power, or a bit of both.

TURBO LAG

Later on in the series we'll look at turbo sizes, but for now, let's get back to turbo lag. Turbo lag is defined as the time between the point when you hit the accelerator and the point at which the turbo produces enough boost to create boost pressure. This may sound like a bad thing but what would happen if you didn't have a turbo? You'd get no boost! So it's either no turbo lag or no boost. A simple choice, I think, especially when you consider that the loss of power due to back pressure caused by the turbine-wheel is hardly noticeable. Provided you haven't done something silly like lower your compression ratio! In years gone by car manufacturers built production turbo motors with low compression ratios to counter the thermodynamic effect of compressing air. Any time air is compressed, the temperature of the air increases. This affects the internal combustion temperatures in the engine. But when a suitable intercooler is used to cool the intake air, normal compression ratios can be used. With normal compression ratios, you're still getting close to normal aspirated performance until you get boost and then you're flying with an up to 50% increase in bhp, depending on the boost you're running! But let's not get too excited just yet, we'll go back turbo boost first.

BOOST PRESSURE

We've said that turbo lag is the time between the point when you hit the accelerator and the point at which the turbo produces enough boost to create above-atmospheric pressure in the intake manifold. The boost level at which the turbo produces enough boost to create above-atmospheric pressure in the intake manifold is called the boost threshold. This is the point at which the exhaust gas flow over the turbine is high enough to overcome inertia and spin the turbine-wheel fast enough so that the compressor-wheel can begin creating boost pressure. From that point on boost will increase but it is important to remember that the quality of the fuel you run and the temperature of the air pumped into the intake manifold will influence the amount of boost you can run. With normal pump fuel, a stock engine and an intercooler, you can safely run at 7-12 psi boost. A wastegate regulates the boost pressure by allowing exhaust gases to pass around the turbine-wheel so as to limit the exhaust gas flow that drives the turbine-wheel.

But more about wastegates at a later stage; here's something to ponder on for now: A properly installed and tuned turbo operating at 10 psi can reduce the 0-60 mph time by a third, despite turbo lag! Yes, you read right a 10 second car will do 6.66 seconds if the turbo is done right!

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