[Dado]

here is some info.

Turbo Water/alcohol Injection - The Theory
Water/alcohol injection relies on the fact that it takes much more energy to raise the temperature of water than it does to lower the temperature of air. The specific heat of a substance is a measure of the amount of energy (kJ) required to increase the temperature of a certain amount of it (kg) by a certain temperature (° C). The specific heat of water is 4.184 kJ/kg ° C. This means that it takes 4.184 kJ of energy to raise one kg of water 1° C in teperature. The specific heat of water is more than four times that of air, which ranges from 1.00 kJ/kg ° C to 1.05 kJ/kg ° C, for the temperatures we're concerned with.

Water/alcohol injection is dependent upon the relative humidity in the atmosphere. Lower humidity will increase the effectiveness of water/alcohol injection.

Advantages to Water/Alcohol Injection
Suppressing Engine Knock. Water/alcohol injection works to suppress engine knock in several ways. First, the water (and alcohol) reduces the temperature of the compressed air. When the exhaust gases are expelled from the combustion chamber, the cylinder, piston, and valve surfaces are at a very high temperature. The water entering the cylinder with the compressed air will work to cool these surfaces and any hot spots which might exist. It is in these hot spots that predetonation would typically occur. As the air is compressed in the cylinder, the water serves to reduce air to fuel contact, reducing the likelihood of auto-detonation. Lastly, if any alcohol is used, it serves to increase the octane of the fuel.
Increasing Intake Air Density. As previously mentioned, the water serves to decrease the temperature of the charged air. Since water/alcohol injection presents no additional flow restriction, this reduction in temperature can only be accompanied by in increase in air density. Also, when the water cools the metal surfaces in the combustion chamber during the intake stroke, this allows more air to enter the cylinder - effectively increasing the volumetric efficiency of the engine.

How Much Water and Alcohol?
Water to Alcohol Ratio. A 50/50 water/alcohol mix is recommended as the minimum, with 70/30 being quite common. In fact, many people use filtered windshield wiper fluid without any modification for a very cheap solution. For our analysis, we'll assume a 70/30 mix, which will have a specific heat of 3.66 kJ/kg ° C (the specific heat of ethanol is 2.43, and methanol is 2.51).
Water/Alcohol to Fuel Ratio. Most experts suggest a maximum water to fuel ratio of 25% and point to many tuning problems with rations this high. Typically, 10-15% water to fuel is a more manageable ratio.

Where to Inject Water
Theoretically, water/alcohol injection can happen anywhere between the air filter and the intake runners. However, injecting water before the turbocharger will damage the compressor wheel. On the other hand, injecting water after the turbocharger is made difficult by the need to increase the pressure under which the water is injected in order to overcome the additional pressure. Also needed is a check valve to inhibit compressed air from entering the water reservoir when water is not being injected, such as in low boost situations. The water should be injected as soon after the turbocharger as possible to allow time for the water to form small droplets. Often, people will inject perpendicular to the tubing to use impact with the back wall of the tubing to further break up the water drops. Alcohol also assists in creating smaller droplets. If water/alcohol injection is to be used in tandem with an intercooler, the water should be injected after the intercooler in order to maximize the temperature drop.

active overcharges, you can build your own for cheap.
http://members.cox.net/stevemonroe/AlcoholInjMod.html
http://www.lehigh.edu/~cak7/Upgrades.../WaterInj.html