Water Injection
Water injection is useful in preventing detonation in supercharged engines that produce more than about ~10 psi of boost. The water injection system is a completely separate system from the fuel injection system.
Typically, the water is mixed with methanol to improve its cooling effect. Mixtures up to 50% work well. Amazingly enough, regular windshield washer fluid works well, as long as you buy the blue stuff. If you can find one that says 50% methanol, 50% distilled water, that is great. Or you can add methyl hydrate to your water.
To set-up a water injection system, you can use a fluid tank, small pump (windshield washer pumps work well), and a Hobbs switchto inject fluid into the inlet tract. This switch closes at a specific pressure, and is installed in the intake manifold. One Hobbs switch is NAPA part# 7011577. This corresponds to a Hobbs part number #76052. It is a normally open 2 terminal switch, factory set to 15 psi. However it is adjustable from 14 psi to 24 psi. Both lower and higher pressure rangesare available from Hobbs 5000 series pressure switches.
An alternative is the Summit Racing “Oil Pressure Safety Switch”. It is made of steel and finished with zinc plating, for just $13. It opens at 7 psi (non-adjustable). Instead of being plumbed to the oil system, you can screw it into the manifold and use boost pressure to turn it on/off. Similar switches are available from Holley (PN 12-810, $20), and Mr. Gasket (MRG-7872, $13).
You need to install a restrictor (~0.030" to 0.050", 0.8 to 1.3 mm) in the line from the pump to the manifold. However, if you have an electrical problem that causes the injection system to stay in the open position while the engine is not running, you can have a "hydraulic lock" which can seriously damage your engine.
Alternatively, you can use a sealed fluid container, pressurized by boost pressure, to inject the fluid. The container must be capable of withstanding the boost your engine will produce. You have one boost line from the intake manifold to the top if the container to supply boost, and a fluid line from the bottom of the container to the compressor inlet to inject fluid. The boost line needs to have a one-way check valve installed so the engine vacuum is not applied to the container. Again, a restrictor is necessary, and it is usually placed on a third “vent” line.
In this case, larger restrictors mean less fluid is injected. This design has the advantage of no moving parts to fail, however it has the disadvantage of injecting the fluid before the intercooler, where there is a possibility it could condense on the inside, rather than flow smoothly to the manifold.
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