Water/methanol injection is a great way to make additional power and add reliability. By injecting a mist of water and/or methanol into the air charge, a motor will run cooler and be more resistant to knock, giving the effect of higher octane fuel. This allows the AFR to be increased, the timing to be advanced, and more power to be made. Having such a system does have one very major drawback: what if it malfunctions or fails? A failure of a water/meth injection system can very easily lead to a blown up motor. This is because with less fuel, more timing, and a sudden absence of methanol, a motor will immediately start to detonate, pre-ignite, and melt pistons. This is where having a good system with good failsafes makes all the difference.
Aquamist/ERL is a company in the UK that makes what is probably the best system out there. Unlike the majority of the other systems, an Aquamist monitors fuel injector duty cycle to inject meth, and does so using the same high speed solenoid valve used by WRC teams. for failsafes there is a water level sensor and a flow meter. The system ties into the stock ecu and boost control system, so if there is a problem with flow or the tank runs dry, boost will automatically be cut or an alternate map will switch on.
How do I know so much about water injection? Well, in the last year I’ve installed over a dozen Aquamist water injection systems. Earlier this year they replaced the HFS-5 with the HFS-6, which is a very much improved kit. We’ve installed and tuned three of them so far.
Here’s an old control box compared to the new version:
As you can see the wiring is much easier on the new system.
A tank and the pump are generally installed in the rear of the car and supply the water/meth to the engine bay. In Subarus I like to run the line under the kick panel next to the fuel lines. In the engine bay it goes to the high speed valve and flow sensor. For the HFS-6, these have been combined into one unit that connects to the board with an RJ-45 connector. The HFS-5 has two separate items that must be wired to the control box individually. Here is the flow control unit mounted in an engine bay:
From the unit, lines go directly to the jet(s) installed in the intake piping. The best placement for jets is after the intercooler, but reasonably far from the TB to allow more time to mix with the air charge. With top mount intercoolers, this is impossible as the IC and TB are inches apart.
Once the system is calibrated the control unit usually ends up tucked away under the center console or in the glove box. To monitor flow is the DDS3 gauge:
It’s pretty dope. The gauge monitors flow, the water level, and activates the failsafe if there is an issue. The three adjusters on the bottom are to scale the gauge and adjust the flow meter. Depending on the line pressure, jet size/quantity, and calibration, the flow will vary. The SC trimmer is used to ensure the max amount of flow falls into the range of the bar display. The WL and WH trimmers determine the window that flow must fall into for the system to operate correctly. If the flow is less than what is expected, a jet could be blocked so the system cuts boost or switches maps. It does the same thing if the flow is more than expected, as this is an indication there is a leak in the line.
As for tanks, there are a couple of good options. The 12l spec-c intercooler tank is great for 02-07 impreza sedans, but the shape unfortunately creates starvation issues when on a race track. To combat this a surge tank is recommended. It’s also common to use the stock windshield washer tank, but they generally only hold about a gallon, and on the race track that doesn’t last long. Howerton Engineering has created a very elegant solution to pump and tank packaging by creating this:
It contains the pump, relay, two 1-gallon tanks, and any excess wiring that ends up in the trunk. Jeff Howerton actually stopped by to visit today to talk about making brackets for mounting the systems in Subarus. I like the Howerton products because they’re simple, reasonably priced, they look good, and they work. How hellafunctional is that?
Well that about sums up the Aquamist HFS-6. Using this system, a turbocharged car will generally make 40-70 additional wheel horsepower and run cooler. With pump gas on a small displacement turbo motor, there is a limit to the power you can make, especially on the 91 we get in California. With Subarus that seems to be at around 400whp. With water/meth injection, you can fill your gas tank with pump gas, and make race gas power.