cant really sum it up better than this... and for a daily drive/non race car its somthing I would probably never think about doing.. Above 500whp with a fwd car theres so many other things you can do that would be more beneficial than meth..$.01
Water Injection:
Water injection is a method for cooling the combustion chambers of engines by adding water to the incoming fuel-air mixture, allowing for greater compression ratios and largely eliminating the problem of engine knocking. This effectively increases the octane rating of the fuel, meaning that performance gains can be obtained when used in conjunction with a supercharger or turbocharger, altered spark ignition timing, and other modifications.
The initial injection of water cools the fuel-air mixture somewhat, which may allow for more mixture to enter the cylinder. But the greater effect comes later during combustion when the water takes in significant amounts of heat energy as it converts from liquid to gas (steam), increasing piston pressure (torque) and reducing the peak temperature with its resultant NOx formation as well as the amount of energy absorbed into the cylinder walls. The duration of combustion is said to be longer.
An interesting side effect that has been reported by some is that water injection effectively "steam cleans" the engine interior, resulting in less carbon residue buildup. Glowing hot carbon deposits are a known cause of knocking.
Fuel economy can be improved with water injection, although the effect on most engines with no other modification, (getting your ECU tuned), appears to be rather limited or even negligible in some cases.
Control over the water injection is important. It needs to be injected only when the engine is heavily loaded and the throttle is wide open; as with other systems which need to monitor engine load, this can be determined by manifold vacuum, which is low when the engine is loaded and high when it is unloaded; however, provision must be made for starting, when the manifold vacuum is also low but water injection is undesirable.
* Reports of more rapid corrosion of the steel and cast iron components of engines to which water injection has been added suggest that more frequent oil changes, particularly when the engine does not experience sustained high temperature operation to evaporate any water from the oil, are prudent.
* Many water injection systems use a mixture of water and alcohol (usually 50/50), partly because the alcohol is combustible, while water is not; in addition, the alcohol serves as an antifreeze for the water.
Methanol & Water Injection:
The water injection section applies here as well, with the following info added in:
Methanol, also known as methyl alcohol, wood alcohol or wood spirits, is a chemical compound with chemical formula CH3OH. It is the simplest alcohol, and is a light, volatile, colorless, flammable, poisonous liquid with a distinctive odor that is somewhat milder and sweeter than ethanol (ethyl alcohol).
Methanol is a high octane fuel (113 octane*) that is extremely resistant to detonation. When using methanol injection, it is advised to mix with distilled water being that under-hood temperatures can turn methanol into steam being that methanol boils at 148.46F (64.7C) - this in turn can cause your car to not inject methanol.
Methanol & water injection is also an effective means of cooling the charge air. Methanol is the preferred alcohol due to its elemental properties (being that it's miscible), and is normally mixed with water to prevent evaporation. Methanol is typically injected before the throttle body.
This both cools the combustion process but adds additional high octane fuel to the fuel air mix raising the effective octane to levels high enough to push knock limited performance to new limits.
Methanol, unlike nitrous oxide or forced induction itself, doesn't add more oxygen to the charge, but by its low evaporation point changes from a liquid to a gas as its introduced into the air charge.
The evaporation process uses the heat from the intake charge to complete the phase change. The alcohol is also a fuel in the charge which will cause a rich condition if used in excess. Due to the lower intake temperatures and denser air charge more power is exerted from the engine.
"Extra" science information:
* Water and methanol are miscible in all proportions. (Miscible is the chemistry term that refers to the property of various substances, particularly liquids, that allows them to be mixed together and form a single homogeneous phase. Substances are said to be immiscible if they cannot be mixed together, for example, oil and water.)
* One of the drawbacks of methanol as a fuel is its corrosivity to some metals, including aluminum. It will eventually totally dissolve aluminum.
* Methanol is not the same as denatured alcohol. Denatured alcohol is ethanol containing a percentage of methanol (to make it unsafe/useless for human consumption but still useful for industrial processes.
