Technical Information

Here's what you need to know about Aquamist Water Injection Systems


Push-on fittings were originally used (from 2002) because it was cost effective and mechanically simple. It was fine until a higher percentage of methanol was added - as much as 100 per cent. It only took a year or so to hear reports that the push-fittings were starting to fail - 'low to severe' leakage. Aquamist responded swiftly and redesigned a family of new compression-type fittings. By 2007, Aquamist replaced all fittings on their systems and the failure reports stopped completely. Sadly, the rest of the industry still clings on to these types of fittings.


Aquamist has designed and made their own jets since 1992. The atomisation effect is produced by a small insert behind the opening; this is called the spinner. It houses a few spiral grooves, directing the water under high pressure in a spiral path before exiting the jet. Our latest jet uses a five-groove spinner instead of two. This improves the evenness and atomisation to no end. Since 2011, Aquamist has offered a large range of jet designs, including some with an inbuilt 15psi checkvalve. The latest CV range comes with an inbuilt 100 micron stainless disc filter.


Aquamist systems provide a constant pressure setting through out the injection cycle - deadhead at 160psi. Aquamist is the only system on the WMI market that runs on constant line pressure. This style of setup can guarantee great atomisation from a few cc to several hundred cc/min. It will of course require an inline Fast Acting Valve (FAV) to complete the task. The response time is only a few thousandths of a second from the PWM signal. This allows highly accurate flow control, identical to the standard OEM fuel injection system. The dynamic range (very low to full spray) is vast and linear. A 160psi constant pressure system is always primed and stored on the upstream side of the FAV. This eliminates any ramp up time compared to the pump speed systems, regardless of the line length. Dribble is almost none as there is no line decompression period.


Aquamist sensors are designed from the ground up and manufactured in house by Aquamist. In 2001, Aquamist started looking for a commercial turbine flow sensor that would meet a specific price criteria. They found one that was made from a plastic body construction. After months of intensive testing, it proved to not be reliable enough for the engine bay environment. So Aquamist designed their very own metal bodied and low friction stainless spindle from the ground up. This all-important device can save your engine from flow issues or simply a few large bubbles in the line. Do not under-estimate the importance of this sensor.


Aquamist reads fuel injector signals rather than a single signal from a MAP or MAF sensor. This is because the F-IDC percentage is the result of multiple sensors and thousands of engineer hours. The fuel flow information is the closest signal to represent true engine load. Some argue that MAP or MAF sensor is as good as F-IDC. It isn't. Boost without RPM reference is meaningless. MAF signal is not linear by design (see image). Some modern GDI engines work very much like a diesel or VW TFSI engines; basically an excess air system. You will be surprised to know that when you're cruising for a short period, the ECU will open the throttle fully while adjusting fuel to maintain the speed. This is to maximise the efficiency of the inlet tract. The ECU will inject more fuel when power is demanded upon overtaking whilst the throttle is still fully opened. So reading the MAF is not accurate at all on modern direct injection engines.


PWM-valve over the pump speed method. Having an accurate engine load signal is pointless if the delivery is not tracking it accurately. Aquamist ruled out using Progressive Pump Speed (PPS) method because it is too slow to respond to engine load changes. This is due to the rotor weight of the pump motor and inertia of a rotating mass. Attached is a chart of Aquamist's FAV/constant-pressure system with a random input (Magenta), flow (Cyan) is mirroring well except we clipped the signal over 90%. Notice there is a 95ms lag due to the response time of the flow sensor. The actual flow delay is in the region of 5-10ms.


How important is it? Only a PWM-valve system can guarantee true linear delivery. This is why all car manufacturers use this method to control fuel flow. Apply a variable voltage to a pump motor and it will give you a linear pressure change. That is where the linearity ends. When a WMI controller sends a 50 per cent duty cycle signal to a 500cc/m system, the system is expected to deliver 250cc/m into your engine - a progressive pump speed (PPS) system will deliver over 350cc/m! Why? Laws of physics rules here: Flow change through a fixed orifice is proportional to the square root of pressure change (see the true response curve of a PPS system below). Why then are other WMI makers still using this delivery method? Answer: circuit design is basic, low production cost and no one seems to know any better.


Aquamist systems do not come with a water tank because there isn’t one size fits all. However we do supply all the parts such as level sensor, in-tank filter and compression fitting and tank bulkhead adaptor. Three jets are supplied with each kit (0.8, 0.9 and 1.0mm), a tee and two adapters as standard. This covers a power range of 350-850bhp. Other sizes are available - size combinations are between 0.4 to 1.2mm. With Aquamist Water Injection Systems, you don’t need to add extra parts to complete a reliable working system. Feel free to contact us if you have any questions.