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Old 02-17-2003, 09:05 AM   #1
fastwrx
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Default Intercooler water spray - when do you use it?

Hi All,

I've done searches on this, but I only come up with discussions about where the water tank is located.

I understand what the water spray DOES - it cools the intake air down after it's been compressed by the turbo (which heats it up) thus concentrating more oxygen for improved combustion and power. Correct me if I'm wrong.

Here's my question: Since it is manually operated... When do I use it? And for how long? From what I understand so far, it's unlikely I'll need it for street driving. But, I do some track days. So, when exactly do I hit the button? And for how long? Will my butt-dyno be able to tell any difference? IOW, what happens when it's turned on? Obviously, it's not like turn on the nitrous , but what effect will I notice?

Thanks!

Mike - Reading these posts makes me very anxious for the arrival of my STi!!
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Old 02-17-2003, 10:46 AM   #2
ANZAC_1915
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See other thread with post from John Felstead.

Track days, and after sitting in traffic.....
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Old 02-17-2003, 10:53 AM   #3
prost893
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Mike, what you described as what the water spray does is actually what the Intercooler itself does. The water spray, through thermodynamic interactions improves the intercoolers effienciency. There was a different thread so I won't go into too much detail here. Suffice to say the coooling comes primarily from heat energy absorded from the intercooler by the water during the phase change from liquid to gas as it evaporates. This has the effect of lowering the temperature of the intercooler and in the process the compressed air inside. Cooler air is more dense so it can produce more power than warmer air.

When to use it? Well, just play with a bit will be your best bet to see how it actually affects the power. I would expect that in very hot conditions you will feel some difference. I can't speak from experience on this so I am speculating. You also should use it when doing track or time events on straight sections where power can build. It would not make much difference in autocross. Really anytime the exterior temp goes really high or you site still for a while it would be helpful.
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Old 02-18-2003, 07:09 AM   #4
WRX 2002
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For autox- I will install a remote switch on the steering wheel so I can dial up addditıonal coolıng while racing. Or fınd a method to keep ıt spraying all the time during the 40 second run. I also will not have to manually spray the IC beween each run.
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Old 02-18-2003, 08:51 AM   #5
fastwrx
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OK, folks... thanks for the info so far.

A couple more questions:

Is the water spray button set up such that it only operates as long as you keep it pushed? Or does it dispense water for a certain amount of time by pushing the button once (and then putting your hand back on the wheel)? Also... How much water is coming out? IOW, is it a RUSH of water, or a fine mist? I'm wondering if it's a LOT of water, is there a possibility of water getting on the exhaust manifold or block and causing a severe thermocycling which could lead to cracks or stressing the metal parts? Just curious. Thanks again. This forum is amazing. I bought my 02 WRX based on the info here, and I ordered my STi for the same reason!

Mike
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Old 02-18-2003, 09:20 AM   #6
WRX 2002
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Fine spray/mist
Each push of the button is 5 seconds (from memory)
Shouldn't cause any problems with exhaust etc
Size of the tank...not sure
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Old 02-18-2003, 10:10 AM   #7
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The "Auto" mode of the standard STi switch works RPM-based. When the tacho needle swings past 4k RPM, the pump is activated and the nozzles will spray water onto the intercooler.

The "Manual" mode simply means you press on the button and the pump is activated.

Each spray lasts around 3 to 4 seconds I think.

I know it is RPM-based because if the car's idling and you rev it up past 4k, the spray will come on. But I don't think it's ENTIRELY RPM-based because IIRC on 1st gear the pump won't activate all the time, especially if you bring up the rev slowly past 4k.

I am NOT sure how the spray works when the RPM is above 4k all the time, but I know it works because on the track (where the RPM hardly falls below 4k) I would empty the standard tank within 15-20 mins.

The (earliest) standard hood-mounted tank holds about 3.8 liters. I'm not sure how much the newer boot-mounted tank holds, but it won't be far off 3.8 liters.

I'm now using the 12-liter Spec C boot-mounted tank, no complaints except it is hard to refill.
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Old 02-19-2003, 07:35 PM   #8
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The water spray does not really cool the air down enough to make more power. It does cool it enough to keep the timing in the right spot, thus resulting in consistent HP.

I recommend installing temp probes on the intercooler and watching the temp. Once the heat soak seems too high, activate the water spray. The evaporation process of the water takes the heat away from the intercooler, and you will see a drop in temps
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