Issue: 81 Section: Technical Features 23 May, 2000

Intelligent Intercooler Water Spray - Part 1Developing the world's best DIY intercooler water spray control system.

By Julian Edgar

To not waste water while still being very effective, an intercooler water spray needs to be use an intelligent, adaptive-learn control system. Here we background the development of the superb (and very cheap!) AutoSpeed / Labtronics intercooler water spray controller. But before we get into the nuts and bolts of the intercooler water spray, you gotta understand how an intercooler works in the first place. Reckon you know that already? You might be surprised....

Intercooler Functioning

It seems straightforward enough. An intercooler acts as an air/air radiator for the intake air, cooling it after the compression of the turbo has caused it to get hot. The compressed air passes through the intercooler, losing its heat to the alloy fins and tubes that form the intercooler core. This heat is immediately dissipated to the outside air that's being forced through it by the forward movement of the car. (We'll get to water/air systems in a moment.)

The trouble with this analysis is that - for a road car - it is not entirely correct. Huh? So what actually happens, then?

I've watched turbo engine intake air temperatures every day for the last 11 years. All have been displayed on digital gauges permanently stuck to the dash of the six different turbo road cars that I have owned - a Commodore VL turbo, Daihatsu Mira turbo, Subaru Liberty (Legacy), C210 RB20DET Skyline, R32 Nissan Skyline GT-R, and an Audi S4. This list includes cars with boost pressures of up to 21 psi (the Mira), air/air intercoolers (GT-R, VL, S4) and water/air systems (Mira, Liberty, C210). And - irrelevantly - the list also includes turbo three, four, five and six cylinders! You might say that I've watched intake air temperature gauges on turbo road cars for more than a quarter of a million kilometres.

So what?

The reason for this build-up is that what follows is likely to be seen as incorrect by many people. For example, someone who measures intake air temps while running a turbo intercooled car for a power pull on a dyno, or who drives it around the block, or who sits back and simply theorises, is almost certain to think that what follows is wrong. But, it isn't.

Heat Sinks

In road cars, intercoolers act far more often as heat sinks rather than as radiators. Instead of thinking of an intercooler as being like the engine coolant radiator at the front of the car, it's far better to think of it as being like a heatsink inside a big sound system power amplifier. If an electric fan cools the amplifier heatsink, you're even closer to the mark.

In a sound system amp, the output power spikes are always much higher than the average power - for example, big output spikes are caused by the beat of a bass drum. Each time there's an output power spike, extra heat is generated by the output transistors and dumped into the heatsink. But because the heatsink has a large thermal mass (it can absorb lots of heat with only a slight temperature rise) the actual working temperature of the transistors doesn't increase much. And because the fan's hard at work blowing air over the heatsink, this inputted heat is then gradually transferred to the atmosphere, stopping the heatsink temp from continuously rising.

Importantly, because the power spike is just that (a spike, not a continuous high output signal), the heat that's just been dumped into the heatsink is dissipated to the air over a relatively long period. This means that the heatsink does not have to get rid of the heat at the same rate at which it is being absorbed.

Now, take the case of a turbo road car. Most of the time in a turbo road car there's no boost occurring. In fact, even when you're driving hard - say through the hills on a big fang - by the time you take into account braking times, gear-change times, trailing throttle and so on, the 'on-full-boost' time is still likely to be less than fifty percent. In normal highway or urban driving, the 'on-full-boost' time is likely to be something less than 5 per cent!

So the intercooler temperature (note: not the intake air temp, but the temp of the intercooler itself) is fairly close to ambient most of the time. You put your boot into it for a typical quick spurt, and the temperature of the air coming out of the turbo compressor rockets from (say) 40 degrees C to 100 degrees C. However, after it's passed through the intercooler, this air temp has dropped to (say) 55 degrees. Where's all the heat gone? Traditionalists would say that it's been transferred to the atmosphere through the intercooler (and some of it will have done just that) but for the most part, it's been put into the heatsink that's the intercooler. The

temperature of the alloy fins and tubes and end tanks will have risen a bit, because the heat's been stored in it. Just like in the amplifier heat sink. Then, over the next minute or so of no boost, that heat will be transferred from the intercooler heatsink to both the outside air - and also to the intake air going into the engine.

Real Life Stuff

All getting a bit complicated? OK, let's take a real-life example. In South Australia (where I live) there's a good, four lane road that climbs a very large hill (for locals - it's Willunga Hill). Many less powerful cars struggle at full throttle to crest the top of the hill at 110 - 120 km/h. Others can manage only 80 or 90 km/h. My Skyline GT-R could top the hill at about 200 km/h, with full throttle and full boost being used for perhaps the prior 30 seconds.

(Only 30 seconds? Another point often forgotten in this debate is: how long can you hold full throttle in a turbo road car? Answer: in the real world, not very long!)

Using a quick-response K-Type thermocouple working with a high-speed digital LED dash meter, I could watch intake air temp, measured to one decimal place. From the bottom to top of the hill, the intake air temp never rose by more than 2 degrees C, and in some cases, often actually fell a very small amount! However, after the top of the hill had been reached and the throttle was lifted, the intake air temp would then typically rise by 5 or even 10 degrees. Why? The stored heat was being dumped back into the engine's inlet air as well as to the atmosphere.

In my Audi S4 (again equipped with a K-Type thermocouple intake air temp display), the smaller intercooler means that once over the top of the same hill, the intake air temp rises by a greater degree - an increase as high as 20 degrees C in fact.

Another example. In my high-boost Mira Turbo I ran a water/air intercooling system. The water/air heat exchanger comprised a highly modified ex-boat multi-tube copper heat exchanger, with a few litres of water in it. An electric pump circulated the water through a separate front-mounted cooling core. Intake air temp was measured using a thermistor and a dedicated LCD fast-response meter.

In normal point-and-squirt urban driving, the intake air temp remained the same with the intercooler pump switched either on or off! Why? Because when the car was on boost, the heat was being dumped into the copper-tube-and-water heatsink, and when the car was off-boost, this heat was fed back into the (now cooler) intake air flow. Of course, if I was climbing a long hill (ie on boost for perhaps more than 15 seconds) the pump needed to be operating to give the lowest intake air temps. But even in that tiny car, 15 seconds of constant full boost would achieve over 160 km/h from a standstill...

The latter shows why water/air intercooling in road cars is so successful - but why most race cars use air/air intercooling. Water has a very high thermal mass, so easily absorbing the temp spikes caused by a road car's on/off boost driving. However, race-style boost (say on full boost for 70 per cent of the time) means that the system has to start working far more as a real-time heat transfer mechanism - which is best done by very large air/air intercoolers.

The key point is that typical road car air/air and water/air intercooling systems act as heat sinks during boost periods at least as much as they act as heat transfer mechanisms.

Water Sprays

In a way the point being made in this article is obvious. When you're testing a car's intercooler, it's common to occasionally stop the test and feel the temperature of the core. If it's hot you know it isn't working very well. And that's because you automatically realise that it is primarily acting as a heatsink! If it was just a radiator, the hotter it was, the better it would exchange heat with the ambient air.....

So, that's a pretty big prelude to the topic of intercooler water sprays, isn't it? But if you've been following along, you'll see that having a spray that switches on only when the engine's on boost is not very helpful. Why? Because you really want the intercooler

core to be cooled before the engine comes on boost, giving a lower temperature heatsink into which more heat can be dumped. This is exactly the same philosophy that sees some turbo drag cars having their intercooler cores sprayed with nitrous oxide to cool them down before a run. If the water spray operates only when on boost, the spray operates too late. But there are also other factors to consider.

Let's look at a real-life example of intercooler water spray control. In the Skyline GT-R, I built and installed a sophisticated dual-nozzle water spray for the large standard air/air intercooler. I initially triggered it from the K-Type thermocouple dash digital display (the one discussed earlier), so that whenever the intake air temperature exceeded 40 degrees, the spray would operate. Result? One rapidly empty 12 litre water tank; no discernible change in inlet air temp! The reason that the water tank emptied so fast is that in urban driving, the intake air temp is often high. This is because the small amount of air being drawn into the engine is rapidly heated by the high under-bonnet temperatures. This meant that in the Skyline's case, the spray was operating even with the car idling in traffic - and the intake air temp did not drop as a result of the spray working. Using a control system consisting solely of an intake air temperature switch simply doesn't work in a road car.

Next, I used a boost pressure switch wired in series with the temperature switch, so that there had to be positive manifold pressure (ie boost) and the intake air temp also had to be over 40 degrees before the spray would operate. Result? Much reduced water consumption, no measurable change in intake air temp! So, using both intake air temperature and boost inputs didn't work very well. Why? Because by the time the spray started to evaporate and cool the heatsink, the boost event was usually all over!

Let me stress again: on a racetrack, or on the dyno, I'm sure that both approaches would have reduced the intake air temp. The water spray would have been operating very frequently or even continuously - therefore, after the first few throttle applications, the spray would in fact be operating before the next dose of throttle. But we're talking about the real world here, not artificial tests. (And another point to remember about the chassis dyno testing of intercoolers - when compared with the car on the road, the ambient airflow passing through the core is wrong in its characteristics of turbulence, speed, temperature and pressure. Great test - I don't think!)

Another real-world problem of intercooler water sprays is that large water tanks are heavy, and also a pain to keep re-filling. So - while water's certainly cheap - a good intercooler water spray system also needs to be as conservative as practically possible in its water use. A single smallish boost squirt in traffic - the intercooler temp low and with plenty of following time to dissipate the heat - does not require that the water spray operate. To spray water in this situation is to simply waste it.

So the key intercooler water spray activation questions become:

How do you set up a control system so that the spray operates before you get on the loud pedal?

And how do you configure it to use as little water as possible?

Intelligent Controls

Obviously there is no way that an intercooler water spray controller can precisely work out what the driver is going to do, before he or she actually does it. For example, the controller can't look ahead during country road driving, realise that a high-speed overtaking manoeuvre is coming up, and cool the intercooler in preparation for it. Nor can it pick when a traffic light grands prix is about to happen - and then react accordingly!

But what it can do is to monitor the behaviour of the driver, picking how hard he or she is driving. If the driver is using lots of power, the water spray can trigger early and maintain a spray for a long period - even during gear changes and on trailing throttles. But if the driver uses just a single burst of throttle, the water spray controller can ignore it, knowing that the intercooler heatsink won't even have started rising in temperature. And if the temperature of the intercooler core is constantly being compared with ambient temperature, an even better picture of what's going on can be realised.

The Labtronics / AutoSpeed intercooler water spray controller actually analyses driver behaviour and intercooler temperatures and then decides exactly when and for how long to work the spray. This approach overcomes most of the control problems listed, and at a very competitive price.

Is it a world first? We think so.....

Summary of Conventional Intercooler Water Spray Control Approaches

Control Technique Advantages Disadvantages

Boost Pressure Switch

Simple, cheap Relatively late switch on Switches off on gear changes, even when

driving hard Switches off on trailing throttle, even when

driving hard Operates even when intercooler is cold May be on continuously during high speed

cruise

Wasteful of water

Throttle Position Switch

Simple, cheap

Early switch-on

Switches off on gear changes, even when driving hard

Switches off on trailing throttle, even when driving hard

Operates even when intercooler is cold

Wasteful of water

Intake Air Temperature Switch

Operates only with high intake air temps

Will continue to operate during gear changes and on trailing throttle

Simple, cheap

In urban driving can be on continuously due to radiator heat soak, lack of engine airflow

Very wasteful of water

Boost or Throttle Position switch plus series Temperature Switch

Operates only with high intake air temps

Can have early switch on

Switches off on gear changes, even when driving hard

Switches off on trailing throttle, even when driving hard

Depending on system dynamics, can be wasteful of water

Hardware Options

The pumps, reservoirs and nozzles that are used can vary widely, depending on how heavy-duty you want the system to be and how much you are prepared to pay for it. Note that the electronic control system is happy operating with either of the following approaches.

1. Heavy Duty

A high-pressure 12-volt pump like a Shurflow or Flojet can be used. These pumps are durable, develop pressures of up to 45 psi, and can be rebuilt if necessary. They're available from agricultural, caravan and boat suppliers. One commonly available pump is the Shurflow 2088-423-244 Multifixture Pressure Pump, that costs about A$110. This pump has a max pressure of 45 psi and an open-flow rate of 10.6 litres/minute. Most of these high-pressure pumps are of the diaphragm type, which makes them a little noisy unless they are rubber mounted. This means that you need to make sure that there is room for a good rubber mounting system (eg a gearbox mount) where you place the pump.

In addition to noise, another problem with these pumps is that many are designed with a built-in pressure switch. This is fitted so that the pump will automatically turn on and off when it is being used to supply a tap. The pump starts when the tap is opened and then stops when the tap is closed - imagine a sink tap in a boat and you get the idea. However, when the pump is used for an intercooler spray, this feature can cause problems, with the pump cycling on and off frequently. A pressure accumulator or pump bypass can be used to reduce this problem.

The intercooler spray water tank can comprise a boat plastic fuel cell - a container that comes with a fluid take-off, large filler facility and good tie-down provisions. A tank of around 10-15 litres is a good compromise of size and practicality for a heavy-duty system. A Scepter high density polyethylene 12 litre tank costs only A$45, with the tie-down strap and support brackets another A$12.

An intercooler water spray system using a diaphragm pump and boat fuel tank will result in a very heavy-duty intercooler water spray. It will also be expensive and relatively bulky. But if you have a high power application - eg race or rally - and the spray will be on very frequently, we suggest you use a diaphragm pump and a large tank of the type described above.

2. Light Duty

However, in most road car applications the heavy-duty type of system is expensive overkill - so we decided to look at a much cheaper solution. Supercharger kit manufacturer CAPA uses an ex-Holden windscreen washer pump and motor as part of the water injection systems in their kits. While in the past we have been very critical of taking this approach (over using a system that has better quality hardware), Tony Rullo of CAPA has assured me many times that his company has never had a pump fail in this application. As a result of this background, we decided to test one of these pumps for durability, flow and pressure. AutoSpeed asked CAPA to make available a pump/reservoir combination to be tested, which they duly did.

While the Holden (VDO, actually) pump could have been simply turned on and left running for a few days, this approach is not at all representative of actual intercooler water spray use. Instead, a sequence of tests was devised that roughly replicated different performance car uses. This on/off test sequence is shown in the table at the end of this article.

The reservoir was filled, the pump connected to a brass Spraying Systems nozzle (more on the nozzle in a minute), which was directed back into the reservoir. Labtronics, partner in the development of the AutoSpeed electronic performance modules, then wrote a software program and developed the hardware to operate the pump in accordance with the test cycle.

To complete each test cycle took about 40 minutes, with 7.5 minutes of that being cycle time and 32 minutes being longer 'rest' times. As described last week, a road-driven forced aspiration car running boost more than 5 per cent of the time is rare - this test made the pump work hard for about 19 per cent of the time, with the worse possible control system being simulated (ie one that causes many on/off sequences). The test ran continuously for more than 350 hours. At the end of that time the pump was still operating without problems, though its current draw had increased marginally and it was a little noisier than at the beginning. However, the test showed that for normal light duty, road car use, this pump and reservoir are quite adequate for an intercooler spray.

The pump (Part No GM90058691) is available from Holden dealers, including a strainer grommet (Part No GMVS20344) on the pick-up. Suitable reservoirs were fitted to late model Commodores - some with short filler necks like the one shown and others with longer necks. The pump suits either. The pump and long neck version of the reservoir are now available in the AutoSpeed Shop. Be aware that this is a good pump - aftermarket cheapies will probably not develop the required pressure.

The Nozzle

In either heavy or light duty systems we recommend that a high quality nozzle be used. While miniature plastic nozzles are available very cheaply from hardware stores, their durability (especially if exposed to engine heat) isn't very high. Instead, it's much better to go for good quality nozzles of the type that you'll find at agricultural supply shops. The US company Spraying Systems is one that has extensive catalogs listing different brass (and engineering plastic and ceramic) spray nozzles that are available - most agricultural spray shops have these catalogs.

A nozzle that is very suitable for intercooler use is the Spraying Systems TX-4 ConeJet spray tip. This nozzle develops a hollow cone, finely atomised spray, with a water flow of about 200 ml/min. Because all the Spraying Systems nozzles are part of a professional system, there are also some pretty good extras available for these nozzles. One useful addition is the 4193A combination filter/check valve, which prevents the nozzle from becoming blocked and also stops it dripping. Different mounting fittings for the nozzles are also available, including bulkhead fittings and adjustable angle swivel fittings.

Even if using a cheap pump, we strongly recommend that you use a good quality, brass nozzle. The effectiveness of the spray at reducing the temp of the intercooler will depend greatly on the size of the droplets produced by the nozzle - and the better the nozzle, the more consistent over its life it will be at producing fine droplet sprays.

Spraying System nozzles are available from larger agricultural supply shops. You will need to specify that you require: the Cone-Jet TX4 spray tip, a 4193A brass strainer check valve, a CP1325 cap, a CP1321T brass body, and a barbed hose fitting to suit 5mm ID hose. They are also available from the AutoSpeed Shop, or, in Australia, by calling Spraying Systems direct on 03 9318 0511 for your nearest stockist.

Pre - Conclusion

The electronic controller will handle pretty well any 12-volt pump. For heavy-duty use we suggest a positive displacement diaphragm pump working with a large tank. For light-duty road car use, a VDO/Holden windscreen washer-based pump and small reservoir are adequate. Whichever approach you take, we strongly recommend the use of a quality Spraying Systems nozzle, though.

We've covered the concepts and we've covered the spray hardware - so what's this gee-whiz controller all about, anyway? Shown above during testing, we reckon that the Labtronics/AutoSpeed intercooler water spray controller is - ahem! - the best DIY controller in the world. It's easy to wire in to place, simple to calibrate - and in bare bones form, nearly as cheap as some pressure switches! However, it's a helluva lot more sophisticated than a switch, that's for sure.

The control system that AutoSpeed and Labtronics have developed has a number of unique features. It:

adaptively monitors how hard the car is being driven; senses the temperature of the day; senses the temperature of the intercooler core; and measures how effective the water spray actually is at reducing intercooler core temp.

The result is an intercooler water spray controller that copes intelligently with almost every condition we can think of. In fact, during testing, at times its operation was almost uncannily good. For example, at high speeds the spray duration is typically much shorter than at low speeds - this is because when you are going faster, the intercooler stays cooler because of the greater airflows. If it's raining, the splashes of water on the intercooler keep it cooler - and so the spray operates far less frequently. Another example - by watching a LED on the electronic module, you can actually see the intercooler heat-soak building up at traffic lights, and also the rise in intercooler temp that often occurs after a boost event. (For more on this intercooler behaviour, see Part 1 of this series).

You soon realise that the times when the intercooler is hot (and so needs the spray to operate when you start driving hard) and when it is cold (no spray needed) are not at all obvious to the driver behind the wheel... let alone to something as primitive as a boost switch.

The Brain

In order to have effective adaptive learn characteristics, the AutoSpeed / Labtronics intercooler water spray controller has to be able to realise when the driver is going for a hard drive. Then, when it figures that the driver is really going for it, the controller keeps the spray on during high loads and during trailing throttle and gear changes. In this hard-driving situation it also switches the spray on very early.

The controller decides that you're going for a Fang by monitoring injector duty cycle - the higher the duty cycle, the greater the engine load.

Don't understand what injector duty cycle is? See the first breakout box.

So why take the approach of monitoring injector duty cycle? There're a couple of pretty good reasons:

no expensive boost pressure sensor is needed, so the hardware is cheaper;

multiple inputs from the airflow meter, throttle position sensor and so on are already incorporated into this signal; if required, the spray can be triggered well before boost even starts to occur; the system is as happy working on cars with programmable management as well as all types of factory EFI.

So why haven't other people used injector duty cycle as the load input on aftermarket controllers? One major reason is that digitally monitoring injector duty cycle in real time is incredibly demanding - Miroslav Kostecki (Labtronics' Chief Engineer) had to do some pretty trick programming of the PIC chip indeed....

While injector duty cycle is used as the major input in deciding when the driver is going for a fang, as you'll see, the controller does a lot more than just switch on the pump at a certain duty cycle. So how does the Fang Factor actually work?

The Fang Factor is initially enabled when a user-adjustable injector duty cycle is exceeded. For the sake of this example, let's say that the owner has set the pot that controls this trip point to a sensitivity that corresponds to 25 per cent injector duty cycle. (Note that you don't actually have to measure duty cycle to set the sensitivity - you just twiddle a pot until a LED comes on whenever you're driving hard!)

For every second that the measured duty cycle exceeds 25 per cent, the Fang Factor trip point is reduced by 2 percentage points (to a minimum of 0). This means that the longer that high loads are used, the more sensitive the system becomes to being tripped.

Okay, but how does the system ever get back to its 25 per cent switch-on point? What happens is that every second that the measured duty cycle is below 25 per cent, 2 percent points are added to the Fang Factor trip point (up to a maximum of 25 in this example). So, at low engine loads, the system is constantly trying to get back to its original setting.

What this all does is make the Fang Factor trip more and more easily as you drive harder and harder. Sound good? It is!

However, there's no point in operating the water spray if in fact the intercooler is not even hot. And the core - acting as a heatsink - won't significantly rise in temperature if boost is being used only for a short burst, or if it's a cold day and the intercooler heat exchanger is so good that it's getting rid of heat as fast as it's being added. To monitor the actual intercooler behaviour, there are two temperature inputs to the controller - one monitoring ambient (day) temperature, and the other, intercooler core temperature. When the intercooler core temp exceeds the day temp by a user-definable amount, the Temp Factor trips.

Only when both the Fang Factor and the Temp Factor are tripped, will the pump switch on.

So that you can see easily what's happening, the status of both the Fang Factor and Temperature Factor can be monitored by watching two LEDs on the control module's PCB. By looking at these LEDs, you can actually see when the controller has decided that you're driving hard, and also when the intercooler temp is starting to rise significantly above the day temp.

Checking the status of these LEDs also lets you easily set the two sensitivity controls - one for Fang Factor and the other for the Temperature Factor.

And there's one other tricky function that also beavers away in the background. During testing it was found that while the spray switched on with great accuracy (ie only when it was really needed), when the boost event was over, it tended to stay on for periods that didn't accurately reflect how hard the car had been driven. To overcome this, we decided to use the temperature sensors to tell the controller how much above ambient temp the intercooler core was at the end of the boost event, and then set the delayed spray on-time from this input. In other words, if the intercooler is still hot after the spray has been operating, it stays on a bit longer. If it's cold, it switches off straight away. How long it keeps running depends on how hot or cold the intercooler is and also on the position of the Temp Sensitivity pot.

All Too Hard!

All sound really complicated? Totally confused? Sure, the internal logic may be complex - but fitting the controller to a car and setting it up is child's play!

There are just two control pots - Fang Sensitivity and Temperature Sensitivity. With the system wired in, you go for a drive. An assistant turns the Fang Sensitivity knob until the Fang LED lights up only when you're driving hard. You get out and feel the temp of the intercooler. If it's at the temp that you want the spray to come on, turn the Temperature Sensitivity pot until the Temp Factor LED just lights up. There - you've finished doing the calibration...

As for the wiring - there're just the two temp sensors (which connect straight to the module), one wiring connection to an injector, power, earth and the relay for the pump. That's it. There are even green LEDs on the board that light up to show you when the right connections have been made - easy!

Control Strategies - Really Nerdy Stuff!

Once injector duty cycle was picked as the primary control input, a great deal of thought was given to how this information should be used. Here's a summary of some of the other approaches considered but then rejected.

Control Approach

Control Details Advantages Disadvantages

Threshold Switching

Pump switches on when duty cycle is greater than a preset threshold (eg 30 per cent). Pump switches off when duty cycle is less than a preset threshold (eg 25 per cent). In this example, there is a hysteresis of 5 per cent.

Simple Early switch on

Hysteresis means no problems of rapid pump cycling

Pump switches off on gear changes and trailing throttle, even when driving hard

Will operate even with a single burst of power

Acceleration Rate and Threshold Switching

Pump switches on when rate of change of duty cycle exceeds a pre-set threshold (eg when duty cycle rises by more than 10 percentage points per second). This would occur during hard acceleration. Pump switches off when duty cycle is less than a simple threshold (eg 25 per cent).

Very early switch on - picks a fang happening almost immediately you leave the line!

If set to be sensitive in lower gears, does not trigger in other gears

If set to be sensitive in high gears, triggers when not needed in lower gears.

Will operate even with a single burst of power

Pump switches off on gear changes and trailing throttle, even when driving hard

Added Simple Delay

Once pump is triggered, it continues to work for a period (eg 10 seconds) after it would normally be turned off.

Pump stays on during gear changes and trailing throttle

Wasteful of water - delay always occurs

Moving Time Window Average

The duty cycle is sampled rapidly. An ongoing average is calculated based on the most recent sample and the average of all of the previous samples. When this average is greater than a preset threshold (eg 30 per cent), the pump switches on. When it is below this threshold, the pump switches off.

Early switch-on Pump stays on during

gear changes and trailing throttle, if the duty cycle average of the power squirt has been high

Conservative use of water

A long sampling time improves 'intelligence' of system but delays the initial switch-on

When it came to installing the intercooler water spray system on my own Audi S4, I decided to take a slightly different approach to that implied in the previous articles of this series. Not because I think that the off-the-shelf kit has anything wrong with it, but because I like keeping my car looking quite standard...and that ruled out adding a new underbonnet water reservoir.

But I'd better start at the beginning.

Installation

The control module installation diagram looks like this:

As you can see, the module needs to be connected to the two temp sensors, to one injector wire, to power and earth, and to the pump. On-board green LEDs show the status of each of the input connections, lighting up when the connections are correct (and when power is on!).

1. The Temp Sensors

Two temp sensors are provided. If you buy the bare bones kit (to see in what forms the spray equipment is available, check the box at the end of this article), you'll get two thermistors that'll then need to be mounted. I started by shortening the wires to the thermistor, and then soldering each of these to a pair of wires running into a long cable.

I then wrapped the joints with heat-shrink, crimped them to the terminal, and then covered the terminal in more heat shrink. This gave an easily mounted, sensitive thermistor. (Don't cover the thermistor itself in heat shrink; that would delay its response time).

The Audi's air/air intercooler core is located in the left-hand front guard, and to access it I needed to temporarily remove the left-hand wheel guard liner. This done, the core was revealed, sitting almost parallel to the road.

The intercooler temp sensor must be mounted with great care - it has to measure intercooler core temp on the back of the core, without the sensor being affected by radiator heat soak, heat from a switched-on headlight, etc. I narrowed the eye terminal with a pair of side-cutters and then slid the terminal down into the fins of the cooler itself. It was wedged in pretty securely, but to make sure that it stayed in place, I added a dob of adhesive.

The ambient air temp sensor needs to be located so that it measures the temp of the outside air going into the intercooler - the temp of the day, if you like. In the Audi's case, this could be done fairly easily - the car uses a ducted intercooler and the sensor was placed at the beginning of this air intake. Again, when locating this sensor, beware of heat-soak from the engine, radiator, etc.

The two sensors were joined to a common 5-wire cable (multi-strand alarm cable bought from an electronics store) that was run back to the control module inside the cabin. The wires were wrapped in tape and care was taken that they wouldn't be subjected to chafing or vibration. (Five-wire cable was used to allow the duty cycle input to be part of the same loom.)

2. The Duty Cycle Input

Talking about the duty cycle input, to pick up this signal, one wire needs to be connected from the module to the switched side of an injector. But how do you work out which is the right injector wire to connect to? (You can pick any of the injectors - but which wire of the pair is the right one to use?) To make things easy, the module will in fact tell you. But since you'll need to have power to the module up and running before you can use this function, we'll come back to it later. At this stage, it's just important to include the extra duty cycle input wire in the loom that you're making. I made the injector wiring connection under the bonnet, which saved having to work out the ECU pin-outs.

3. Power and Earth

Power should be of the ignition-switched variety, and the earth - well, that just means any chassis point on the car.

4. Pump Relay

The relay wiring connections act just like an on/off switch, so connect the pump to the relay in the way shown in the diagram. The relay can handle 10 amps - so if you're using a monsta pump, check its current rating to make sure the current draw doesn't exceed this figure. If it does, you'll need to use another, separate power relay.

5. Powering-Up the System

With all the connections made but for the duty cycle input, apply power to the module. The Power On green LED should light, as should the Intercooler Temp OK and Ambient Temp OK LEDs. If the Power LED does not light up, check the power supply connections. If either of the temp LEDs stays dark it means that there is either a break or short circuit in these connections. Next, connect the duty cycle input wire to one wire of an injector. When this wire is connected correctly, the Duty Cycle OK LED will turn on and stay lit. If the LED is dark, or lights up only briefly then goes out, swap the wire to the other side of the injector. When the car is being driven along, all four green LEDs should be lit - four greens means that all the inputs are OK!

6. The Reservoir and Pump

No matter which way I orientated the Holden/VDO water reservoir (described in Part 2) in the Audi's engine bay, it was a tight fit. Worse still, the only space available meant that it would have to be mounted directly above the ABS Hydraulic Control Unit (not great if the reservoir leaked) and also on very long brackets (not so good when the 2.5 litre container will have a mass of over 2.5kg when full). If the container absolutely had to go in here then it would... but was there another, better way?

I liked the look of the standard windscreen washer container - at 4.4 litres it was big, it fitted the available space (funny that!), it contained an inbuilt strainer on the fill cap, and it also had an audible and visual indicator on the dashboard to show when its fluid got low. Could I add another pump to this reservoir - one just for the intercooler water spray?

I pulled the standard reservoir out and discovered to my joy (yep, joy!) that it had been designed to take another pump - probably for the rear window washer of the wagon version of the Audi 100. Even better than that, after drilling just one hole, the Holden/VDO

pump clicked straight into place - it was obviously the same pump that the reservoir had been designed to accommodate in the first place. Gotta be lucky sometimes I suppose....

This meant that the pump could be seamlessly integrated under the bonnet, without any sign of its presence being visible.

7. The Spray Nozzle

Given that the car uses a ducted intercooler (ie outside air is fed to the core through a specific passage), the obvious place for the spray was in this air intake duct. (But of course located well after the ambient air temp sensor!) I used a Spraying Systems TX-4 hollow cone spray, a filter/check valve (the latter very important in stopping the nozzle constantly dripping when it's mounted below reservoir level), and mounted the nozzle on a new bracket.

While it's shown here without the lower grille in place, the spray nozzle assembly fitted behind the normal grille so again, it stayed invisible. The spray covers the core evenly with water, and because of the ducted intercooler construction, all of the sprayed water has to pass through the core - there's nowhere else for it to go.

Calibration

What position you set the Fang Sensitivity and Temperature Sensitivity pots to will depend on a whole host of factors eg:

How big the intercooler is; how much water you're spraying; how big the water reservoir is and how often you want to re-fill it; how big your injectors are; what boost level is being used; and how early boost comes on.

Rather than trying to work all of this out, it's a lot easier to simply set the pots on a trial-and-error basis. In the Audi, I set the Fang Sensitivity pot so that when a touch more than usual acceleration was being used, the Fang LED would light. So, normal acceleration away from the traffic lights didn't illuminate it, but pushing just a bit harder (like maybe you want to change lanes and you need to get in front of someone) would cause it to turn on.

I set the Temp Sensitivity pot so that when the intercooler was warm to touch (about 10 degrees C above ambient) the Temp LED was lit up. These simple settings worked pretty well in practice - and of course can be easily changed if I decide that either factor comes into action a little early or a little late.

One point: if you live in a land of no speed limits, or if you tow a boat fast, make sure that at constant high speed both the Fang and Temp LEDs are not lit together (and so the pump LED is switched on). Of course, that will only happen when you're using a lot of throttle and the intercooler is hot (and so maybe it's much too small anyway), but in this situation you may have the spray running continuously, causing the reservoir to empty too quickly. When the controller is set correctly this shouldn't be a prob - eg with the Fang and Temp settings described as above, my Audi can be driven at a constant high speed without the Temp LED staying on, because the intercooler stays pretty cool with the extra airflow.

  Trips Earlier(turn anticlockwise)

Trips Later(turn clockwise)

Fang Factor Will turn on at lower engine loads Will turn on at higher engine loads

Temp Factor

Will turn on at lower intercooler temps

Will keep spray on longer after boost event is over

Will turn on at high intercooler temps

Will keep spray on shorter time after boost event is over

Remember - both the Fang and Temp LEDs need to be lit before the pump will switch on.

Note that the Temp and Fang adjustment pots are of the 25-turn type, giving excellent calibration sensitivity.

Testing

As outlined in Part 1 of this series, an intercooler water spray can only be correctly tested on the road. Road testing gives an accurate flow of cooling air, correctly creates heat-soak and other conditions, and gives real-life engine loads. Testing of the Intelligent Intercooler Spray was carried out on the Audi, which runs a standard 1 Bar of boost - a peak pressure that occurs at as low as 2000 rpm. To see what was going on, the actual intake air temperature on the Audi was continuously monitored with a fast-

response K-Type thermocouple, read off on the AutoSpeed TempScreen (see "TempScreen: Part 1 - Installing the Intake Air Temp Probe" )dashboard LCD display.

Unfortunately, as the intercooler spray was developed during winter, full hot weather testing could not be carried out - summer is likely to show the system performing even better than in the test results covered here. However, on a 20 degree C day, full-load acceleration runs were undertaken through the gears from 0-160-0 km/h, followed by a U-turn and then an immediate repeat run to a higher speed: 0-180-0 km/h.

With the intercooler water spray working, the maximum intake air temp (recorded from the probe mounted directly after the intercooler) was 33 degrees C. When the water pump was disabled, this skyrocketed to a peak of 49 degrees C, with a temp of 42 degrees C held through most of the acceleration runs. That's a stunning decrease in intake air temp that occurs with the spray working.

Because the Intelligent Spray Control Module was left connected all of the time (just the pump circuit was disabled in 'no-spray' mode), looking at the module's Temp LED showed that when the water spray was working, the intercooler core came down in temp far faster than when the spray was not. Without the spray working, the core stayed hot for several minutes after the boost event was over, but when the spray had been working, the core was reduced to near-ambient temps after about 30 seconds.

In short, the spray system substantially reduced on-boost temps and also caused the intercooler to cool down far more quickly.

The 'intelligent' aspect of the control system also works very well. When the intercooler is cool (eg after a few kilometres of light-load cruise) the spray will not turn on even when you boot it - not until the core starts to heat up, anyway! On the other hand, when the core is hot, the spray will trip instantly when more throttle is used - and, if the core is not dropping quickly enough in temp - it will also keep the spray on even after the throttle is released. Driving along in cruise mode - followed by a quick burst of throttle - will not turn the spray on, but about 30 seconds later you will see the Temp LED come on as the heat-soak from that boost event gets the whole intercooler warm. Hit the throttle then and the spray triggers instantly.

In cool weather you can spend an hour driving around an urban area, squirting off every set of traffic lights - and the spray doesn't trigger once. The Fang Factor LED will light as you accelerate away - but the Temp LED's off because the intercooler is still cool. A few moments later, the Temp LED will light as the intercooler is warmed right through - but by that time you've throttled back and so the Fang LED's gone off. Driving in these sorts of conditions shows the enormous water savings possible - a boost pressure switch would have triggered the spray perhaps 20 times but the intelligent controller hasn't switched it on even once. That can cut by 80 per cent or more the number of times you need to refill the water tank.... And of course, if the intercooler doesn't drop enough in temp between those boost squirts, the spray will immediately trigger - and will then have a delayed on-time that's proportional to how hot the 'cooler core actually is.

The Fang learning behaviour can also be seen - drive the car hard for more than about 20 seconds and by looking at the Fang LED, you'll be able to see how early the Fang Mode trips into action when you again put your foot down.

If you're into the technology, it's all pretty cool watching those LEDs tell the story of what's happening. If you're not, that's fine - the system is working without any supervision anyway.

Conclusion

AFAIK, this is the first system in the world to monitor injector duty cycle as an input into an aftermarket control system. Add to that the ability to learn short-term driver behaviour, and measure actual intercooler and ambient temps, and it's a system that's damn good. Especially at this price...