Incidentally, the standard pump fitted to the Legacy is a twin speed item and switches to high speed 15 lpm(3.5 gpm) when required.

After several days of colourful language, I managed to fit the heat exchanger and plumb in the pump (mounted in the nearside front wheel arch) and run hose to the oil cooler in front of the air conditioning condenser. I also wired the pump to run directly from the battery (via the fuse) with a 40 Amp relay being switched from the ignition.

After filling the system with water, I inserted the fuse and switched on the ignition.

Great! The water was circulating at a very tidy rate of knots and I was happy – apart from one small point, the "Water Puppy" was howling for all it was worth…. Without exaggeration, the water pump made more noise than the engine. I tried experimenting with sound deadening material and rubber isolating feet but to minimal effect. The noise was also amplified somewhat by enclosing the pump in the wing.

After driving around for a couple of weeks, scaring people who thought they were being overtaken by a washing machine on full spin cycle, I decided to get expert help……

Being impressed with the build quality and performance (but not the noise) of the Jabsco unit, I contacted them and was referred to one of their UK agents, Cleghorn Waring. Speaking to their sales department, was a memorable conversation:

After the shock of the initial discussion, I found their Sales department to be very friendly and extremely knowledgeable on the Jabsco range. I then realised that my initial choice had been entirely inappropriate and was recommended two suitable pumps for the task:

The small 3 gpm "Circulation" pump for £76+VAT or a 17gpm "CentriPuppy" (18510-0020 - with "Carbon Ceramic" seal for higher temperatures) for £175 + VAT. Don’t fight it, I thought - I went for the big one....
Once it had arrived (along with the adapters from Think Automotive to convert the 3/4" ports on the pump to the 5/8" hose) and been fitted, it has proven to be a much better choice – it is very quiet and the flow of water is smoother reducing cavitation (bubbles) I now know….

The pump is fitted in the driver's side wing (RHD) and is suspended "upside down" under where the air filter is mounted. The "CentriPuppy" can be fitted either horizontally or vertically with the ports at the bottom but is not self-priming so it needs to be mounted low with gravity providing the water supply.

Anyhow, now experiencing driving in relative tranquility, I began testing the new system to see how it performed.

The air/water intercooling system should be more efficient in normal road driving due to the much higher heat sink capability of water over air. Water apparently absorbs four times the amount of heat that air does but it is worth bearing in mind that the water supply is finite (in my case now about 6 litres or 1.5 gallons in total) as opposed to an air/air which has an infinite supply of air to cool itself. Therefore, in road use when boost is used occasionally (for overtaking etc) and the average speed is fairly low, the air/water should be a better method. Using it on a track, the water will not get a chance to cool down between periods of boost and may result in being less efficient than an air/air unit. This obviously makes the size of the radiator important - the larger it is, the quicker the water cools down again.

For driving in cities and urban areas, I would expect very good gains from the air/water system but if your average speed is higher then it would be a much closer run thing compared to a good air/air unit. Weight is another important consideration as an air/air unit will almost certainly be lighter.

Well, that's the theory, what about in practice. When I tested my car, there was an immediate improvement in performance when driving from cold (after allowing the car to warm up) but as a journey progressed, the improvement seemed to drop off as the coolant increased in temperature. After a few weeks and some "head scratching" I came to the conclusion that there wasn’t sufficient water in the system to work effectively.

I therefore asked Forge Motorsport to construct a custom aluminium tank for me which acts as a reservoir and is fitted in front of the air filter. This is a very snug fit and is in the area used by the ABS in later models. This added 4.5 litres approximately (1 gallon) to the system capacity and cost around £110 (including VAT and delivery).

Further testing ensued and although the rise in temperature was much slower, ultimately the coolant was still taking far too long to cool down again when heated. After some further on-line discussion and good advice, I realised that a better radiator was called for.

I subsequently commissioned Pace Products to create a custom radiator for me using their 18mm (3/4") thick water core. This was sized to cover approximately half the frontal area of the air con condenser (the other half being used partially by the Mocal transmission cooler I had fitted soon after purchasing the vehicle). The radiator is as tall as physically possible, resting on the lower cross member. This is again a very snug fit but has the advantage of not requiring major modifications to the bumper (apart from bending the inner lip very slightly by a few millimetres). The front grill however has been "butchered" to allow the water connections and brackets to fit:

 

Now with the improved cooling, the intercooler is working how I imagined although it still takes a while to cool down if parked for a while before continuing a journey. The system seems to deal well with any heat generated to keep intake temperatures below 35 degrees C (95 degrees F). Depending on the ambient temperature, on a run the intake air stabilises at a set temperature and doesn’t deviate by more than 3 degrees C (37 degrees F).

 

A couple of weeks later, I also bought some Samco blue flexible coolant hose (with an embedded wire helix to prevent "kinking") which allows much tighter bends than the Moquip stuff. This removed the less than ideal bend radius of the hose onto the radiator outlets and visibly increased flow. This could have been avoided if I had asked Pace to provide right-angled hose connections on the radiator - hindsight is a wonderful thing!

The coolant circuit changed a few times during testing and needed to be re-thought completely when changing from the self-priming pump to the gravity-fed one. The final system is shown below in this very rough diagram:

Water drops downwards from the reservoir to the pump inlet (green line). The pump is actually located under the reservoir and air filter but has been moved slightly in the diagram to try to help clarity.

The coolant then leaves the pump outlet passing to the radiator inlet (yellow line). After cooling, the cold water (shown as a blue line) leaves the radiator and along the hose suspended under the radiator to the metal feed pipes bolted to the inlet manifold. The metal feed pipe leads to the cold water inlet of the heat exchanger.

After absorbing heat from the intake air, the hot water outlet follows a similar route (red line) travelling from the heat exchanger, through the other metal feed pipe, in the second hose under the radiator and into the reservoir, passing through the wing.

As you can imagine, the drivers-side wing (RHD) is fairly busy with three coolant pipes and the pump now in there, along with the existing cold air intake for the engine. The area behind the headlight is also rather congested with three coolant pipes passing into the wing using the convenient large inner wing access hole!

I have also replaced the front number plate with a "stick-on" bonnet item which should reduce the obstruction to the front radiator.

The lessons learnt here (by me) are:

** Ask for advice when buying specialist equipment (i.e. pumps).

** Do NOT neglect the radiator (which I had read was "the least important part of the system…") – bigger really IS better!

The Future

The only immediate thing I want to address is the fitting of a good size fan although finding one which is slim enough (25mm) is proving a real challenge – I did say it was a snug fit !

I am currently using "Water Wetter" in the intercooler coolant after getting good results in the main engine coolant. This should increase efficiency even further…

Apparently, nitrous oxide also has a strong air cooling effect….

 

Other Interesting Links

http://www.racetep.com/atoliq.html - scan of the page in the Spearco manual regarding Air/Water chargecoolers

http://www.protherm.demon.co.uk/page29.html – rather nice thermometer (AKO14721) with 2 user programmable (high) temperature relays which I have in my car!

http://www.netcomuk.co.uk/~gavinp/dyno2.gif – the effect of all of my mods (after being parked for an hour!) - compared with the standard unmodified car. The figures are power at the wheels (all 4 wheels driven).

http://groups.yahoo.com/group/Air-Water-Intercoolers - E-mail group for Air/Water Intercoolers

http://home.ccci.org/Key_Information/MerkurPage.htm - Turbocharged XR4I air/water experiences

http://www.paceproducts.co.uk/ricc/anatomycc.htm - Pace Products "Anatomy of a chargecooler" page

http://www.22b.com/own_theodore.htm - Details of Theodore Soutzos's old car (a 22B with a chargecooler)

http://www.e30m3performance.com/myths/more_myths1/Water_Wetter/water_wetter.htm - Interesting discussion about "Water Wetter"

http://www.autospeed.com/A_0436/page1.html - Autospeed article about Ford's patent for using air con to cool the water in an air/water chargecooler.

 

 

All pictures remain the copyright © of the relevant owner. If you wish to contact me for any reason, please drop me a mail at gavinp@netcomuk.co.uk. Close-ups of Subaru Heat Exchanger courtesy of tom@kartboy.com. Photos of the water pumps, courtesy of © Jabsco Inc. Intercooler fan picture © Zerosports .

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