Cycling the Squirt

Over the years we’ve covered a number of ways of triggering intercooler water sprays – from our very sophisticated and effective Intelligent Intercooler Water Spray module, right through to cheap and cheerful boost pressure switches. But all of the simpler (and cheaper) methods tend to waste water – and nothing is more painful than having to frequently fill the intercooler spray tank. But the new approach covered here lets you substantially reduce water consumption, in addition to gaining other benefits.

Why You Want It

Whether it’s triggered manually by a dashboard switch or automatically through the action of a boost pressure switch, intercooler water sprays tend to do one thing rather effectively. What’s that, you say? They cool the intercooler? Well, if the spray uses a high pressure pump and a good quality nozzle that produces a fine mist of drops, they do that all right.

But the other thing that they do really well is use lots of water!

It’s a bit of a quandary. If you throttle-down the water flow (say by using a small plastic garden irrigation tap), the pressure at the nozzle will also fall, resulting in a dribble - not a mist of tiny droplets. And take it from us, a dribbling intercooler water spray is very close to having none at all... Sure you can fit a smaller nozzle, but there’s a limit to how small you can go while keeping the cost of the nozzle low and still generating small drops. In other words, if you want to use a widely available, cheap nozzle, you’re limited in how low you can go in flow.

So what’s the answer, then? It’s simple – when you’re on boost, run the pump for short bursts every few seconds. For example, if you can cycle the pump for 2-second bursts every 5 seconds, you will immediately save a helluva lot of water. In fact, in this example your water consumption will be more than halved. You still have the high pressure, small droplet spray that you need, but with less overall water flow.

But won’t the spray then become ineffective? Not likely! You see, most intercooler water sprays provide more water than actually evaporates, anyway. That’s why if you look at the intercooler immediately after the spray has been running under boost conditions, nine times out of ten, the intercooler is still dripping.

If you spray in short squirts it still cools the core very well, but it dramatically cuts water consumption. It’s why the rare factory cars with intercooler water sprays use only short bursts of water, not a continuous spray.

How To Do It

So, how do you control your water spray pump in this way? Supervising the squirting action of the water pump is an electronics kit - the Auto Timer, developed by Silicon Chip electronics magazine. Electronics engineer John Clarke did the design and development. The kit (and the book in which it is featured) are available from the AutoSpeed Shop and Jaycar stores. The Auto Timer kit costs AUD$40 - we introduced it last week at The Auto Timer.

The first step is to build the kit and then test that it works. Follow the instructions carefully – in fact unless you are a experienced electronics kit builder, we suggest that you buy the High Performance Electronics for Cars book which contains a range of projects (including this one), covers the background in engine management, and shows how to build electronic kits.

As you will see from the book, the Auto Timer can be configured in different modes: One-Shot (ie it times a period whenever it is triggered) or Pulsing (it cycles on and off after being triggered). The Pulsing mode can also be further configured to give varying on and off times – from example, being on for 2 seconds and then off for 5 seconds, on for 2 seconds and off for 5 seconds, (etc). (Sound familiar?)

Obviously it’s this Alternating mode that we need to use in the intercooler spray application.

After configuring the timer in this mode, it’s easy to set how long the spray is on for, and how long it is off for. Basically, you just dial it up on the rotary switches. The only limitation is that the biggest ratio that you can have between on and off times is 9:1, for example, on for 1 second and off for 9 seconds. However, it’s unlikely that you’d want to go so short in ‘on’ time anyway.

The Wiring

The Auto Timer has a double pole, double throw relay output – so it’s dead easy to connect up the pump. One of the relay’s Normally Open connections is connected to ignition-switched 12V while the adjacent Common is connected to the intercooler water spray pump. The other side of the pump is earthed. That means that when the relay clicks over, the pump turns on, spraying water out of the nozzle. The on-board relay can handle 5 amps, so even quite large spray pumps can be directly driven.

To trigger the timer, the signal input wire is connected via a switch to 12V. When that switch is closed, the pump will start pulsing on and off. The switch can be a manual one mounted on the dashboard or it can be a boost pressure switch. The current carried by this switch is tiny so it also allows very sensitive low-current boost pressure switches to be used.

In this application (a 1988 Maxima V6 Turbo), a fast-response LCD inlet air temperature display (see LCD Temp Display!) has been fitted to the car. This allows the real-time viewing of intake air temp. This information, along with driver decisions about load, required performance, etc, are used to decide when it’s best to manually turn on the spray via a dashboard switch.

Setting Up

The length of time that you have the pump pulsed on for will depend on a number of factors, including the presence or otherwise of a check valve in the water plumbing. In the case of the Maxima, a spray nozzle has been fitted that has a check valve installed directly behind the spray orifice. (The nozzle is available from the AutoSpeed Shop – see AutoSpeed Spray Nozzle Kit.) The check-valve prevents water flowing back to the pump when the pump is not running, and so reduces the delay before spraying starts when the pump is first switched on. Without this check-valve, the minimum ‘on’ time of the pump would have to be increased. That is, if the pump ran for only 2 seconds at a time, without the check-valve water might come out of the nozzle for only the last 0.5 seconds.

But you don’t really need to worry much about the theory - seeing all this is pretty easy if you set some times on the rotary switches of the timer and then just watch what happens at the spray end of things. For example, you could initially try an ‘on’ time of 4 seconds and an ‘off time’ of 8 seconds, and then make adjustments from there. It’s also easy to place a light on the dashboard so that you can see when the spray has been triggered by the boost pressure switch (or as a reminder than you’ve manually switched it on). The LED that’s mounted on the PCB can either be moved to the dash (make sure you keep its polarity correct) or you can wire a 12V pilot light in parallel with the pump.

The Results

In the Maxima the efficiency of the water spray had never been in question – but especially when climbing long country road hills (which I frequently do), the consumption of water had been much higher than was originally expected.

Extensive testing of the pulsed spray was carried out up a large country road hill, where the car is on high boost for about a minute continuously. After testing various combinations of water spray ‘on’ and ‘off’ times, it was found (at least in winter!) that the spray could be run for only 1 second every 7 seconds without negatively affecting the measured intake air temps. (And of course it’s easy to change this just by altering the rotary switch positions – perhaps have summer and winter settings?)

That means that in this application, the spray water consumption has been decreased by an astonishing 85 per cent with no measurable increase in intake air temp! To put it another way, if you currently need to fill your intercooler spray bottle once a week, with the pulsing spray modification that will almost certainly change to once every 6-8 weeks or so....

Mission accomplished!