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The main function of water injection systems is to suppress detonation caused by high temperature and pressure developed within the combustion chamber when the effective compression ratio has been taken beyond the auto-ignition point by either a turbo or a supercharger. Water, with its high latent heat content, is extremely effective for controlling not only the onset of detonation.

This is from the Devils Own site: In a piston engine, the initial injection of water cools the fuel-air mixture somewhat, which increases its density and hence the amount of mixture that enters 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). This increases piston pressure (torque), reduces peak temperature and resultant NOx formation, and reduces the amount of heat energy absorbed into the cylinder walls. The alcohol in the mixture burns, but at a much slower rate than gasoline. The net result is that the combustion process happens slower, preventing the destructive supersonic shockwave characteristic of detonation.


To walk through the installation of this water injection kit click the first picture in the gallery below, then click Next. Notes to installer will appear below the pictures.

WaterInjection-IMG_0159.jpg: 1010x758, 158k (August 28, 2009, at 09:11 PM)
This is the engine bay as before the installation.
WaterInjection-IMG_0160.jpg: 1010x758, 165k (August 28, 2009, at 09:11 PM)
This is the kit. The author did not opt for a bottle as he had limited room.
WaterInjection-IMG_0161.jpg: 1010x758, 123k (August 28, 2009, at 09:11 PM)
Remove the airbox to gain access to the bolts for the ABS system.
WaterInjection-IMG_0162.jpg: 1010x758, 122k (August 28, 2009, at 09:11 PM)
The ABS was adjusted and relocated slightly more linear to give the room for the DEVILS OWN pump.
WaterInjection-IMG_0163.jpg: 1010x758, 103k (August 28, 2009, at 09:11 PM)
Another view of the new pump next to the ABS.
WaterInjection-IMG_0164.jpg: 1010x758, 89k (August 28, 2009, at 09:11 PM)
This is the Relay for the whole thing. Mounting location chosen was on the bolt that holds the Boost solenoid on.
WaterInjection-IMG_0165.jpg: 1010x758, 80k (August 28, 2009, at 09:11 PM)
The wiring is then done and some neat cable covering used.
WaterInjection-IMG_0166.jpg: 1010x758, 98k (August 28, 2009, at 09:11 PM)
The unit is activated by this boost switch. It is adjustable so you can have the injectors come on whenever you like. Mine is set to 16psi.
WaterInjection-IMG_0167.jpg: 1010x758, 136k (August 28, 2009, at 09:11 PM)
Supply for the boost switch was taken from the capped port on the inlet manifold. The kit is supplied with a TEE so you can cut into another vac line.
WaterInjection-IMG_0168.jpg: 1010x758, 155k (August 28, 2009, at 09:11 PM)
So now all the pump and electrics are done and the car is ready to have the nozzle fitted and the supply.
WaterInjection-IMG_0169.jpg: 1010x758, 124k (August 28, 2009, at 09:11 PM)
Washer bottle was removed, drilled an 11/16 hole and tapped it. The elbow was then attached to the feed pipe.
WaterInjection-IMG_0170.jpg: 1010x758, 124k (August 28, 2009, at 09:11 PM)
Take the intercooler off and drill another hole 11/16ths and tapped that too. Nozzle was placed in the elbow of the intercoler pipe, this is where three different people recommended is best for Subarus. It is a bit fiddly but solid once there.
WaterInjection-IMG_0171.jpg: 1010x758, 138k (August 28, 2009, at 09:11 PM)
This is the nozzle set up. This installation is running a .35 nozzle and a one way valve on the whole system.
WaterInjection-IMG_0172.jpg: 1010x758, 97k (August 28, 2009, at 09:11 PM)
Finally with the intercooler back on, the feed pipe is attached and all ready for the road.


Lay the pipe on the windscreen to set the boost switch first. The author set it somewhere near then drove down the road, watching the boost gauge, till the nozzle started spraying. Once it was set, re-fitted the nozzle.

Installers First Impressions

First impressions are that boost could be raised to 1.5bar, and the knock sensor is saying all ok. The major thing to be noticed is that on full boost the temperature drop is only around 7 degrees. Usually you might expect a temp after the intercooler of anywhere between 14-18c. On the authors installation the intake temperature is 22c, the pre-intercooler temperature is 24c, and before the water injection comes on, post intercooler is around the 15-17c mark. In summery, it makes a major improvement, not only that, the car has no detonation at all AND the author was running it all on 95 at the time.

Information Source - SIDC forum thread, republished with permission, Water Injection System Fitted, With pics

Page last modified on August 24, 2008, at 10:12 AM
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