The main components of any water injection system are a pump, nozzle, and a trigger device. All other parts make the system more automated, complex and expensive. You need to decide what you need and can do without when you build your system. My goal was to design a system that would work during most driving situations with the least amount of driver interaction.

The system described here has 2 stages with three injectors. Although three injectors proved to be too much for my application, it may be not in yours. For most situations one main injector and a RPM injector will work well.

This system will inject based on throttle position and rpm's. A variable voltage regulator is attached to the throttle. The voltage range is 0v at idle to 7v at WOT. That voltage is then fed into a control box. The control box uses the regulators voltage as a reference to control a 0-12v output to the pump to vary the water pressure for injection.

The control box that I use is from Snow Performance. It was originally attached to the MAF sensor which has a variable voltage of 0-5v. My GM MAF sensor uses frequency rather than voltage output so a converter had to be used in-between which didn't’t work. So, I modified a voltage regulator and fixed it to the throttle.

An RPM switch is used to open a second solenoid for an additional injector. Keep in mind that you will want to be either in passing gear or near WOT when that solenoid is opened. The pump should be as close to full voltage as possible to overcome the loss of overall pressure in the lines when that solenoid opens.

A lever switch attached to the throttle activates the main solenoid. It is wired to a 12v relay using the 87 and 87a outputs. When you are not on the pedal, the 87a output of the relay opens a solenoid that relieves pressure in the lines. When you are on the gas, the lever switch opens and the 87 output of the relay closes the pressure relief solenoid and opens the main feed solenoid to the injectors. The reason for this set up is that after I came to a stop light or slowed down in traffic, there was still pressure in the lines and the water would still be spraying into the intake. It caused stalling and bogging. Using a relay to control the solenoids solved the problem.

I used 14ga wire for most of the wiring to the switches, relays, solenoids and control boxes. All connections are soldered together and heat shrink tubing covers each. I cannot stress enough the importance of good solid connections. Take your time and be meticulous. It will save you a lot of trouble in the end and will ensure a long lasting, reliable system.

INSTRUCTIONS

The Pump
	This is the single most important piece.  Some injection sites are selling 150 – 200 psi pumps.  This is completely over kill for our situation. I use a ShurFlo 100psi pump and even this is a little too much. Since we don’t need nearly as much water as a forced induction vehicle, the pump will pulse on and off because it has reached the 100psi limit. Not only is this annoying but it also shortens pump life. One web site, http://www.rbracing-rsr.com/waterinjection.html suggests using a ShurFlo 60 psi bypass: Model 8000-543-220.  It has an internal by-pass valve that keeps the flow and pressure steady.  I would suggest you read the information they have on their site.  If I had to build another system I would use this pump.
	I used the typical 100psi ShurFlo pump. There is an pressure adjustment screw in the center of the head. I turned the pressure down as far as it could go.

Nozzles
	There are several types and sizes of nozzles on the market. I bought mine at a supply house called McMaster-Carr.  In that site, enter misting nozzles in the search box. Other injection sites sell the same nozzles for 5x the price. Still, other injection sites use what look like custom machined nozzles. What ever you choose, be prepared to spend some time making it fit to your application. There is a lot of pressure behind that nozzle and a high potential for a leaks. I used 90° fittings to make an injector. The nozzles have a fine mesh screen that does not quite fit inside of the fitting. In order to get the nozzle as flush as possible with the inside of the intake tube, I drilled out the center of the fitting to get the nozzle it to fully fit inside.
	This is an overhead view of a 90° Female Elbow 1/4" NPT push on connector. In order for a nozzle to screw inside, the center will have to be drilled out on a drill press because the nozzle will bottom out with hardly a turn.
	This is a side by side comparison of the fittings drilled out. The metal is soft brass and will bind up the drill bit in a second. Keep it in a clamp and go slow. Make sure you are dead on center or else you will end up hitting the "O" ring seal and ruining the whole piece. When your done, the nozzle should thread in almost all the way. Do not over tighten or else you will damage the fine mesh screen on the nozzle.
	Depending on the thickness of the tube, you may need to use a washer to take up some of the space so you don't bottom out the nozzle in the fitting.
	This is a side view of the nozzle and fitting installed in the intake tube.
Filter
	This is a 10 micron fuel filter from CNC Motor Sports It is absolutely necessary to have a filter on a water injection system. The last thing you want is to have a clog.

Hose

Almost all of injection sites use the same hose, polyethylene. It comes in many colors and is very solvent resistant. The size of choice is ¼”. The selection of fittings for this size of hose is fantastic. I purchased 100ft and after setting everything up, I have used almost all of it. Knowing that you have that much to play with gives you the freedom to place everything exactly where you want it.

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