Water Injection

Unfortunately I was unable to squeeze in the pipework for an intercooler, lack of room! So I decided to go for water injection, this isn't as good as an intercooler at cooling the air but it has some advantages. There is a great deal of information on Water Injection Systems on this Forum. The recommended amount of water to be injected is 10 - 15 % of the fuel. An educated guess tells me my engine will use around 15 gph at 5750 rpm on boost. This meant I needed a 1.5 - 2.25 gph water injection system. The trouble was, most good systems are fairly expensive, especially the type that control the flow rate with boost. So I searched the Internet and found a site where someone had built his own system(Link here). He uses an adjustable Shurflo water pump and a Nitrous nozzle. My thinking was to add some form of control to this system, that would allow me to vary the amount of water depending on boost. When I priced everything up it was so much cheaper than a ready made system and it was in keeping with my theory of doing as much as possible on a DIY basis. So I sourced the pump from Northern Tool Equipment (pt/no 2687) £75 and decided to get a proper nozzle from Aquamist, (0.6mm) £15.

I drilled and tapped a 1/4" BSP thread into the side of the washer bottle so as it will feed the pump and also added a float switch in the side. This will light up an LED on the steering column cover when the water gets low. Space for the Sureflo pump was difficult to find, but fortunately I hadn't added anything on the chassis rail just behind the radiator, so I made a bracket up to fit it onto that.

Thumbnails of Pump, bracket and water container.

I had several ideas on the flow control side of things; one was to slowly increase the voltage to the pump as boost increased; another was to pulse a valve between 80-100% duty cycle depending on boost. But after chatting on the WI forum I was convinced that a much easier way was to drive a fast acting valve at the same rate as the fuel injectors.

Thumbnail of Water injection nozzle position in Intake

So I started to modify the basic MSnS code. First I added Dave Edge's Target AFR idea, as this worked very well on MS. Then I added some code to switch on Water Injection. This comes on when boost is above the set value in MT (user defined 121). When this is reached the Pump is turned on via X2 and X3 is pulsed at the same rate as the injectors. The theory being that if the water nozzle is selected to give a 15% flow rate of the total of the injectors flow rate then it follows that it should naturally give the right amount of water. All 8 injectors together give me a total flow of 1760 cc/Min of fuel. So if I select a 260cc/Min water nozzle and fire it with the same signal as the injectors then it should be very close to ideal. I may have to alter the pressure or mess around with nozzles a bit to fine tune it, but it should be close. The output X3 is driving a FET which in turn switches the fast acting valve from Aquamist (PtNo 806 244 £110+vat). Both water injection outputs are switched off if the throttle is suddenly closed. Whilst the water injection is on the O2 sensor is ignored, as the water would upset the readings.

Circuit Diagram available here

Diagram of Water Injection available here

You can download the .asm file here and the .h file here. You will need this ini file for MT2.16 from here or modify your own.

I would highly recommend putting a light on the dash to show the water pump is powered up, I put one on the top of the steering column cover.

I've also written a slightly different code for controlling the WI, this takes into account the inlet air temperature, so water will not be turned on untill manifold pressure and IAT are above a preset value. Once water is turned on it then waits for boost pressure to drop below the set level, despite what the IAT is reading, as this should drop as soon as water is injected in. This code also ignores O2 readings once the water is on.

You can download the .asm file here and the .h file here. You will need this ini file for MT2.20 from here or modify your own.

I had a real problem finding Methanol to mix with the distilled water, so in the end I opted for straight distilled water.