Can anyone give me the lowdown on when best to use the intercooler water spray on my sti, and what to put in it (i know water) but should it be distilled?

 

As you probably know it is to cool the air charge down. The air is hottest at full boost so this is the time of most benefit to use the sprayer. ie. giving it stick.

A lot of people will tell you to use distilled water. It does prevent the white scale but this scale takes so long to build up and is easy to clean so I never thought it worth the hassle. Tap water was just fine.

If you want more cooling power use 30/70 Methylated Spirits/Water. Just don't tell the insurance and keep it away from the exhaust.

When I get a 22B I'll use Evian or similar though.