Can anyone answer this question for a newbie owner of a MY95 WRX Sti? What's the purpose of the in-car waterspray, when do I need to use it, what happens if I don't? Is it a gimmick?

Thanks in advance

 

Hi the waterspray sprays water on the windscreen so u can see though it

no seriously (Although I'm sure to be corrected), the spray sprays water onto the intercooler cooling the air into the engine giving you a burst of power and apparantly, yes, it does make a difference

shame my uk turbo doesn't come with one well i suppose mine does clean the window

 

Rather than giving a burst of power, it helps the car to keep on producing peak power over longer periods. Basically, the intercooler is like a big heat sink which absorbs & dissipates heat from the VERY hot air being pushed out by the turbo. The cooler the inlet charge from the turbo, the denser it is, and the more power you can produce.

Problem is that when you're caning the car over a rally stage, everything (including the intercooler) gets hot. So the intercooler loses some ability to absorb heat, which means a hotter inlet charge, which means power will drop off. The water spray applies an extra cooling medium (evaporation) to the intercooler, helping it to cool down, which means it can absorb more heat, meaning cooler inlet charge and restoring full power.

This also means that if you want max power, you need to start to use the spray BEFORE you start caning it, to cool the IC down as much as possible before you start heating it up again.