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All you should know about Water Injection/build your own.

bottom link seems dead. here's what the wayback machine had to say :

Designing A Water Injection System

This explanation was provided by John G. Gauthier.

Please read the DISCLAIMER

Atomized water (or water/alcohol mix) sprayed into the incoming air stream of a motor drastically decreases the air temperatures. A DSM with a side mount intercooler, temps at the throttle body while at full boost can reach approximately 300 degrees (give or take). With a front mount, maybe 250ish. With FMIC and water injection, 175 isn't unheard of. (these numbers are all approximate, every motor is different.)

I should point out that water injection does not equal more horsepower, but it leads to more horsepower:

And think about this: 1 more psi of properly supported boost (appropriate air flow, fuel supply, good spark, etc.) means 10-15 horsepower.

Determining System Requirements: For anyone building a water injection system from scratch, you first need to determine your water requirements. Aquamist suggests 10% to 25% water to fuel. Since I know my figures by heart, we'll use mine as an example.

Fuel injector size X number of cylinders X maximum duty cycle = fuel system size

550cc/min X 4 X 95% = 2090cc/min of fuel

Now, I wanted approximately 20% to 25% water to fuel, so 20% of 2090 = 418cc/min of water. Aquamist rates their nozzles as follows:


Aquamist nozzles

Differential pressure: 5bar (73psi) 7bar (102psi)
0.4mm nozzle provides 120cc/min 150cc/min
0.5mm nozzle provides 150cc/min 200cc/min
0.6mm nozzle provides 175cc/min 250cc/min
0.7mm nozzle provides 195cc/min 300cc/min
0.8mm nozzle provides 215cc/min 330cc/min
0.9mm nozzle provides (not given) (not given)
1.0mm nozzle provides (not given) (not given)

Each nozzle has a flow rate at 5bar and at 7bar of differential pressure. Differential water pressure is determined by subtracting boost pressure (at peak) from the water pressure provided by the water pump. In my case, I have the ShurFlo 100psi (~7bar) water pump and I run 22psi (~1.5bar) of boost on the street, so my effective water pressure (aka differential pressure) is about 5.5bar.

See for converting between different pressure measurements.

Two 0.8mm Aquamist nozzles together would flow a little more than 430cc/min of water which is right inside the 20% to 25% window I was looking for. The first nozzle was placed just after the turbo to help my front mounted Greddy intercooler operate more efficiently, while the second nozzle mounted on my throttle body elbow helps lower the cylinder temperatures.

My Parts List:

Stock 2G DSM windshield washer bottle (used as water tank) $FREE
ShurFlo 100psi 12VDC pump $80 (product information)
NAPA low pressure switch $25
Aquamist 4mm vinyl hose $2.75/meter (product information)
Aquamist pressure accumulator $40
Aquamist solenoid $50 (product information)
Aquamist one-way check valve $14 (product information)
Aquamist 0.8mm nozzles (2) $16/each (product information)
Radio Shack switches, wire, relays, etc ~$25

Total system cost, ~$250-300

This pic only shows one nozzle but you get the idea:

The pump draws fluid from the bottom of my stock 2G DSM washer bottle in the trunk. (why Mitsu put it there, we may never know but it's over one gallon, placed beneath the spare tire, supplying both the front & rear washers.) The ShurFlo 100psi pumps are self-regulating, meaning that they start to pump when they see less than 85psi and continue to pump until they feel 100+psi then stop (they also come in 40, 60, and 150 psi variations.) There's a 4mm line from the pump to under the hood. Once there, it meets a brass 'T' to a pressure accumulator and a solenoid, mounted in the stock 2G battery location. The accumulator provides a larger volume for the pump to pressurize, allowing the pump to be on longer and less often giving the pump a longer life expectancy. The pressure solenoid provides a large volume for the pump to fill, thereby allowing the pump to run for longer but less often (leading to longer pump life.) The solenoid is controlled via the pressure switch, set to 8psi of boost pressure. After the solenoid, I have one 0.8mm nozzle 6" after the turbo, and the second 6" before the throttle body. The distance from the solenoid to the throttle body nozzle is approximately 6" and straight up, so I didn't use a check valve. However, since the post-turbo nozzle is over a foot away as well as downhill, there's a check valve 1" before the nozzle. The Aquamist check valves have a ~1bar or ~14psi 'crack' pressure to flow in the correct direction. This prevents dripping or small leaks. Going in the wrong direction it's something insane like 15 or 20bar...

I chose 8 psi simply because with my driving style, if I hit 8 psi I'm on my way to WOT 22 psi. Less than 8 psi is just around-town driving for me. The NAPA pressure switches are adjustable from 5 to 50 psi, so pick what you need.

The advantage of a pressurized system like this is that full pressure is available instantly at any time. The other option is to control the pump directly and not use a solenoid, but there's a much longer reation time involved and since the pump is being constantly turned on and off the pump's life expectancy won't be as long.

Here's what I observed running on 93 octane w\ S-AFC (not DSMLink):

18 psi, Non-water injection run:
2nd gear, 20 degree timing peak
3rd gear, 20 degree timing peak
4th gear, 15 degree timing peak

20 psi, 10% Water injection run: (just one nozzle, pre-TB)
1st gear, 21 degree timing peak
2nd gear, 20 degree timing peak
3rd gear, 17 degree timing peak

22 psi, 20% Water injection run: (both nozzles)
1st gear, 22 degree timing peak
2nd gear, 24 degree timing peak
3rd gear, 23 degree timing peak

Since the injected water lowers the cylinder temperatures, detonation is pushed back and knock is reduced, thereby allowing the ECU to increase ignition timing. If you noticed, I started with 18 psi + no water injection and ended up with 22 psi + 20% water injection. On 22 psi, I actually have more timing than on 18 psi!

Inside the cockpit I have a few LEDs and switches mounted in the center console to give me some feedback on the system's current status:

Red LED = system off
Small green LED = pump is currently pumping
Large green LED = nozzles are currently spraying
First switch = entire system off / entire system on
Second switch = nozzles off / nozzles on

Since the pump is self-regulating, the pump may or may not be on at the same time as the nozzles, hence two different LEDs. The first switch controls the pump as well as the nozzles such that should it be turned off the second switch's position doesn't matter. First switch on and second switch off means the system will maintain pressure but will not inject water.

Online response:
That ... water injection system taps into your washer fluid
reservoir, right? So what the hell am I supposed to spray
on my windows?

I drilled a small hole in the bottom of my washer bottle and put in a 1/2" nippled barb. My stock washer pumps are entirely intact and operating, completely unaffected. Oh and distilled water by itself does just fine as a windshield solvent.

Online response:
I couldn't run water injection up here in the winter; I'd
have a solid block of ice in my reservoir. That idea just
isn't going to fly.

I should point out that I live in Michigan right now, just off Lake Superior. I should also point out that I am running water injection right now, in the dead of winter. If you want to run water injection up here in the winter, you have two reasonable options:

Option 1) Go out and buy yourself a gallon of isopropyl alcohol and mix it 50% / 50% with pure distilled water. Will not freeze, and in fact you'll even run better than straight distilled water since the isopropyl alcohol has a small combustive quality. Only thing you have to be careful of is that most pumps (ShurFlo included) can be corroded by alcohol or other harsh chemicals, hence it must be diluted with pure distilled water.

Cost, about $10 per gallon for a 50%/50% mix. Isopropyl alcohol by itself is at cheapest (and trust me I looked) $10 a gallon. Then add the price of distilled water.

For what it's worth, the water / alcohol mix does work GREAT as a windshield washer solvent, but at this price I'd avoid getting your windshield dirty.

**NOTE : the isopropyl mix is typically used on track days due to it's mildly combustible yet easy to acquire nature (any pharmacy.) **

Option 2) Go out and buy yourself a nice one gallon jug of blue windshield washer fluid. NOT PINK, NOT DE-ICER, just the cheap BLUE junk you can get at any gas station. Average contents, 49.999% distilled water, 49.999% alcohol, and 0.002% blue dye. See where this is going? It won't freeze, it cleans your windshield just fine, it's cheap as hell, it's has a tiny combustive quality, and 0.002% blue dye has no effect. I am one of about a hundred guys on the DSM Water Injection list, many of whom run or have run washer fluid.

Cost, about $0.95 per gallon.


For the record, obviously depending on how I drive, I go through about half a gallon of water per 16 gallon tank of gas.

Other Examples of Possible Water Injection Systems (neither have been created yet):

For my friend Matt's 1998 Grand Prix GTP (supercharged 3.8L V6), his fuel system totals 1900cc/min across total for six cylinders. 10%-25% would be 190cc to 475cc. Since getting to the cylinder intake for all six might not be that easy, an injector or two at the throttle body would be the best choice. Probably two 0.7mm nozzles, one at 1/2 boost and one at 3/4 (and controlled on a switch, maybe even with a WOT throttle switch.)

For my brother Larry's 1998 Acura Integra GS-R (normally aspirated 1.8L), his fuel system totals... what... 960cc/min? 240cc/min injectors? 10%-25% would be 96cc to 240cc. Here installing on the intake runners would be easy but injectors aren't made small enough. Sorry Larry. /ubbthreads/images/graemlins/wink.gif But an intake injector somewhere just after the filter would be ideal, plenty of time for the water to atomize prior to hitting the cylinders. Control will be trickier but not too bad; figure a small (0.5mm) nozzle with a WOT sensor and/or connected with VTEC's engagement. Which, now than I think about it, isn't a bad idea. Nozzle is on at WOT or VTEC (or both obviously.) Hmmmm.... With water injection you can have VTEC kick on sooner and keep everything safe...

Water Injection Parts Suppliers:

-- Aquamist parts --

Georges Imports Ltd, ask for Brad
8011 State Line Road
Kansas City, MO 64114
[email protected]

-- ShurFlo parts --

Pro Spray Equipment
1616 Marlborough Ave.
Riverside, CA 92507
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